The document serves as an introductory guide to functional programming in Go, authored by Eleanor Mchugh. It covers essential programming concepts such as imperative programming, conditional loops, enumerate ranges, and functions as values, providing code examples for clarity. The tutorial emphasizes practical coding techniques based on the author's extensive experience in the field.

1. AN
INTRODUCTION
TO
FUNCTIONAL PROGRAMMING
IN
GO
ELEANOR MCHUGH

2. ELEANOR MCHUGH
@feyeleanor
APPLIED PHYSICIST
MISAPPLIED HACKER
EMBEDDED SYSTEMS
VIRTUAL MACHINES
DIGITAL IDENTITY
RUBY
GO

3. LEANPUB://GONOTEBOOK
A GO DEVELOPER'S NOTEBOOK
▸ teaches Go by exploring code
▸ free tutorial on secure networking
▸ opinionated but not prescriptive
▸ based on a decade of experience
▸ buy once & get all future updates
▸ very irregular update cycle
▸ the only book I'll ever write on Go

4. LEANPUB://GONOTEBOOK

5. IMPERATIVE
PROGRAMMING

6. A SIMPLE TASK
0: 0
1: 2
2: 4
3: 6
4: 8

7. IMPERATIVE
PROGRAMMING
THE CONDITIONAL LOOP

8. THE CONDITIONAL LOOP
package main
import "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
fmt.Printf("%v: %vn", i, s[i])
}
}

9. THE CONDITIONAL LOOP
package main
import "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
fmt.Printf("%v: %vn", i, s[i])
}
}

10. THE CONDITIONAL LOOP
package main
import "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
fmt.Printf("%v: %vn", i, s[i])
}
}

11. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

12. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

13. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

14. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

15. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

16. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

17. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

18. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

19. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

20. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

21. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

22. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

23. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

24. THE CONDITIONAL LOOP
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i := 0; i < len(s); i++ {
Printf("%v: %vn", i, s[i])
}
}

25. IMPERATIVE
PROGRAMMING
AN EXCEPTIONAL LOOP

26. AN EXCEPTIONAL LOOP
package main
import . "fmt"
func main() {
defer func() {
recover()
}()
s := []int{0, 2, 4, 6, 8}
i := 0
for {
Printf("%v: %vn", i, s[i])
i++
}
}

27. AN EXCEPTIONAL LOOP
package main
import . "fmt"
func main() {
defer func() {
recover()
}()
s := []int{0, 2, 4, 6, 8}
i := 0
for {
Printf("%v: %vn", i, s[i])
i++
}
}

28. AN EXCEPTIONAL LOOP
package main
import . "fmt"
func main() {
defer func() {
recover()
}()
s := []int{0, 2, 4, 6, 8}
i := 0
for {
Printf("%v: %vn", i, s[i])
i++
}
}

29. AN EXCEPTIONAL LOOP
package main
import . "fmt"
func main() {
defer func() {
recover()
}()
s := []int{0, 2, 4, 6, 8}
i := 0
for {
Printf("%v: %vn", i, s[i])
i++
}
}

30. AN EXCEPTIONAL LOOP
package main
import . "fmt"
func main() {
defer func() {
recover()
}()
s := []int{0, 2, 4, 6, 8}
i := 0
for {
Printf("%v: %vn", i, s[i])
i++
}
}

31. AN EXCEPTIONAL LOOP
package main
import . "fmt"
func main() {
defer func() {
recover()
}()
s := []int{0, 2, 4, 6, 8}
i := 0
for {
Printf("%v: %vn", i, s[i])
i++
}
}

32. AN EXCEPTIONAL LOOP
package main
import . "fmt"
func main() {
defer func() {
recover()
}()
s := []int{0, 2, 4, 6, 8}
i := 0
for i := 0; ; i++ {
Printf("%v: %vn", i, s[i])
i++
}
}

33. IMPERATIVE
PROGRAMMING
ENUMERABLE RANGES

34. ENUMERABLE RANGES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

35. ENUMERABLE RANGES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

36. ENUMERABLE RANGES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

37. ENUMERABLE RANGES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

38. ENUMERABLE RANGES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

39. ENUMERABLE RANGES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

40. PROGRAMMINGWITH
FUNCTIONS

41. PROGRAMMINGWITH
FUNCTIONS
ENUMERATION BY FUNCTION

42. ENUMERATION BY FUNCTION
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s []int) {
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

43. ENUMERATION BY FUNCTION
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s []int) {
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

44. ENUMERATION BY FUNCTION
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s []int) {
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

45. ENUMERATION BY FUNCTION
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s []int) {
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

46. ENUMERATION BY FUNCTION
package main
import . "fmt"
func main() {
print_slice(0, 2, 4, 6, 8)
}
func print_slice(s ...int) {
for i, v := range s {
Printf("%v: %vn", i, v)
}
}

47. PROGRAMMINGWITH
FUNCTIONS
TYPE ABSTRACTION

48. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
for i, v := range s.([]int) {
Printf("%v: %vn", i, v)
}
}

49. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
for i, v := range s.([]int) {
Printf("%v: %vn", i, v)
}
}

50. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
for i, v := range s.([]int) {
Printf("%v: %vn", i, v)
}
}

51. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
if s, ok := s.([]int); ok {
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

52. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
if s, ok := s.([]int); ok {
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

53. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
if s, ok := s.([]int); ok {
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

54. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
if s, ok := s.([]int); ok {
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

55. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case []int:
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

56. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case []int:
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

57. ABSTRACTING TYPE
package main
import . "fmt"
func main() {
print_slice([]int{0, 2, 4, 6, 8})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case []int:
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

58. PROGRAMMINGWITH
FUNCTIONS
FUNCTIONS AS VALUES

59. FUNCTIONS AS VALUES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(s, element)
}
func element(s []int, i int) int {
return s[i]
}
func print_slice(s []int, f func([]int, int) int {
defer func() {
recover()
}()
for i := 0; ; i++ {
Printf("%v: %vn", i, f(i))
}
}

60. FUNCTIONS AS VALUES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(s, element)
}
func element(s []int, i int) int {
return s[i]
}
func print_slice(s []int, f func([]int, int) int {
defer func() {
recover()
}()
for i := 0; ; i++ {
Printf("%v: %vn", i, f(i))
}
}

61. FUNCTIONS AS VALUES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(s, element)
}
func element(s []int, i int) int {
return s[i]
}
func print_slice(s []int, f func([]int, int) int) {
defer func() {
recover()
}()
for i := 0; ; i++ {
Printf("%v: %vn", i, f(s, i))
}
}

62. FUNCTIONS AS VALUES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(s, element)
}
func element(s []int, i int) int {
return s[i]
}
func print_slice(s []int, f func([]int, int) int) {
defer func() {
recover()
}()
for i := 0; ; i++ {
Printf("%v: %vn", i, f(s, i))
}
}

63. FUNCTIONS AS VALUES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(s, element)
}
func element(s []int, i int) int {
return s[i]
}
func print_slice(s []int, f func([]int, int) int) {
defer func() {
recover()
}()
for i := 0; ; i++ {
Printf("%v: %vn", i, f(s, i))
}
}

64. FUNCTIONS AS VALUES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(s, element)
}
func element(s []int, i int) int {
return s[i]
}
func print_slice(s []int, f func([]int, int) int) {
defer func() {
recover()
}()
for i := 0; ; i++ {
Printf("%v: %vn", i, f(s, i))
}
}

65. FUNCTIONS AS VALUES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(s, func(s []int, i int) int {
return s[i]
})
}
func print_slice(s []int, f func([]int, int) int) {
defer func() {
recover()
}()
for i := 0; ; i++ {
Printf("%v: %vn", i, f(s, i))
}
}

66. PROGRAMMINGWITH
FUNCTIONS
CLOSURES

67. CLOSURES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(func(i int) int {
return s[i]
})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
}
}

68. CLOSURES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(func(i int) int {
return s[i]
})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
}
}

69. CLOSURES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(func(i int) int {
return s[i]
})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
}
}

70. CLOSURES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(func(i int) int {
return s[i]
})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
}
}

71. CLOSURES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(func(i int) int {
return s[i]
})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
}
}

72. CLOSURES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(func(i int) int {
return s[i]
})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
}
}

73. CLOSURES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(func(i int) int {
return s[i]
})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
}
}

74. CLOSURES
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_slice(func(i int) int {
return s[i]
})
}
func print_slice(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
}
}

75. PROGRAMMINGWITH
FUNCTIONS
CONCURRENCY

76. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for i := 0; i++; i < 5 {
c <- i * 2
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

77. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for i := 0; i++; i < 5 {
c <- i * 2
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

78. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int, 16)
go func() {
for i := 0; i++; i < 5 {
c <- i * 2
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

79. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for i := 0; i++; i < 5 {
c <- i * 2
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

80. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for i := 0; i++; i < 5 {
c <- i * 2
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

81. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for i := 0; i++; i < 5 {
c <- i * 2
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

82. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for i := 0; i++; i < 5 {
c <- i * 2
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

83. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for _, v := range []int{0, 2, 4, 6, 8} {
c <- v
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

84. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for _, v := range []int{0, 2, 4, 6, 8} {
c <- v
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

85. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for _, v := range []int{0, 2, 4, 6, 8} {
c <- v
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

86. CONCURRENCY
package main
import . "fmt"
func main() {
c := make(chan int)
go func() {
for _, v := range []int{0, 2, 4, 6, 8} {
c <- v
}
close(c)
}()
print_channel(c)
}
func print_channel(c chan int) (i int) {
for v := range c {
Printf("%v: %vn", i, v)
i++
}
return
}

87. PROGRAMMINGWITH
FUNCTIONS
INFINITE SEQUENCES

88. INFINITE SEQUENCES
package main
import . "fmt"
func main() {
c := make(chan int)
go sequence(c)
print_channel(c)
}
func sequence(c chan int) {
for i := 0; ; i++ {
c <- i * 2
}
}
func print_channel(c chan int) {
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, <- c)
}
return
}

89. INFINITE SEQUENCES
package main
import . "fmt"
func main() {
c := make(chan int)
go sequence(c)
print_channel(c)
}
func sequence(c chan int) {
for i := 0; ; i++ {
c <- i * 2
}
}
func print_channel(c chan int) {
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, <- c)
}
return
}

90. INFINITE SEQUENCES
package main
import . "fmt"
func main() {
c := make(chan int)
go sequence(c)
print_channel(c)
}
func sequence(c chan int) {
for i := 0; ; i++ {
c <- i * 2
}
}
func print_channel(c chan int) {
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, <- c)
}
return
}

91. INFINITE SEQUENCES
package main
import . "fmt"
func main() {
c := make(chan int)
go sequence(c)
print_channel(c)
}
func sequence(c chan int) {
for i := 0; ; i++ {
c <- i * 2
}
}
func print_channel(c chan int) {
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, <- c)
}
return
}

92. INFINITE SEQUENCES
package main
import . "fmt"
func main() {
c := make(chan int)
go sequence(c)
print_channel(c)
}
func sequence(c chan int) {
for i := 0; ; i++ {
c <- i * 2
}
}
func print_channel(c chan int) {
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, <- c)
}
return
}

93. PROGRAMMINGWITH
FUNCTIONS
WORKING WITH KINDS

94. WORKING WITH KINDS
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
case []int:
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

95. WORKING WITH KINDS
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
case []int:
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

96. WORKING WITH KINDS
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
case []int:
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

97. WORKING WITH KINDS
package main
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := s.(type) {
case func(int) int:
for i := 0; i < 5; i++ {
Printf("%v: %vn", i, s(i))
}
case []int:
for i, v := range s {
Printf("%v: %vn", i, v)
}
}
}

98. WORKING WITH KINDS
package main
import "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := reflect.ValueOf(s); s.Kind() {
case reflect.Func:
for i := 0; i < 5; i++ {
p := []reflect.Value{ reflect.ValueOf(i) }
Printf("%v: %vn", i, s.Call(p)[0].Interface())
}
case reflect.Slice:
for i := 0; i < s.Len(); i++ {
Printf("%v: %vn", i, s.Index(i).Interface())
}
}
}

99. WORKING WITH KINDS
package main
import "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := reflect.ValueOf(s); s.Kind() {
case reflect.Func:
for i := 0; i < 5; i++ {
p := []reflect.Value{ reflect.ValueOf(i) }
Printf("%v: %vn", i, s.Call(p)[0].Interface())
}
case reflect.Slice:
for i := 0; i < s.Len(); i++ {
Printf("%v: %vn", i, s.Index(i).Interface())
}
}
}

100. WORKING WITH KINDS
package main
import "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := reflect.ValueOf(s); s.Kind() {
case reflect.Func:
for i := 0; i < 5; i++ {
p := []reflect.Value{ reflect.ValueOf(i) }
Printf("%v: %vn", i, s.Call(p)[0].Interface())
}
case reflect.Slice:
for i := 0; i < s.Len(); i++ {
Printf("%v: %vn", i, s.Index(i).Interface())
}
}
}

101. WORKING WITH KINDS
package main
import "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := reflect.ValueOf(s); s.Kind() {
case reflect.Func:
for i := 0; i < 5; i++ {
p := []reflect.Value{ reflect.ValueOf(i) }
Printf("%v: %vn", i, s.Call(p)[0].Interface())
}
case reflect.Slice:
for i := 0; i < s.Len(); i++ {
Printf("%v: %vn", i, s.Index(i).Interface())
}
}
}

102. WORKING WITH KINDS
package main
import . "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := ValueOf(s); s.Kind() {
case Func:
for i := 0; i < 5; i++ {
p := []Value{ ValueOf(i) }
Printf("%v: %vn", i, s.Call(p)[0].Interface())
}
case Slice:
for i := 0; i < s.Len(); i++ {
Printf("%v: %vn", i, s.Index(i).Interface())
}
}
}

103. WORKING WITH KINDS
package main
import . "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := ValueOf(s); s.Kind() {
case Func:
for i := 0; i < 5; i++ {
p := []Value{ ValueOf(i) }
Printf("%v: %vn", i, s.Call(p)[0].Interface())
}
case Slice:
for i := 0; i < s.Len(); i++ {
Printf("%v: %vn", i, s.Index(i).Interface())
}
}
}

104. WORKING WITH KINDS
package main
import . "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := ValueOf(s); s.Kind() {
case Func:
for i := 0; i < 5; i++ {
p := []Value{ ValueOf(i) }
Printf("%v: %vn", i, s.Call(p)[0].Interface())
}
case Slice:
for i := 0; i < s.Len(); i++ {
Printf("%v: %vn", i, s.Index(i).Interface())
}
}
}

105. WORKING WITH KINDS
package main
import . "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
defer func() {
recover()
}
switch s := ValueOf(s); s.Kind() {
case Func:
for i := 0; ; i++ {
p := []Value{ ValueOf(i) }
Printf("%v: %vn", i, s.Call(p)[0].Interface())
}
case Slice:
for i := 0; ; i++ {
Printf("%v: %vn", i, s.Index(i).Interface())
}
}
}

106. WORKING WITH KINDS
package main
import . "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := ValueOf(s); s.Kind() {
case Func:
for_each(func(i int) {
p := []Value{ ValueOf(i) }
Printf("%v: %vn", i, s.Call(p)[0].Interface())
})
case Slice:
for_each(func(i int) {
Printf("%v: %vn", i, s.Index(i).Interface())
})
}
}
func for_each(f func(int)) (i int) {
defer func() {
recover()
}
for ; ; i++ {
f(i)
}
}

107. WORKING WITH KINDS
package main
import . "reflect"
import . "fmt"
func main() {
s := []int{0, 2, 4, 6, 8}
print_values(s)
print_values(func(i int) int {
return s[i]
})
}
func print_values(s interface{}) {
switch s := ValueOf(s); s.Kind() {
case Func:
p := make([]Value, 1)
for_each(func(i int) {
p[0] = ValueOf(i)
Printf("%v: %vn", i, s.Call(p)[0].Interface())
})
case Slice:
for_each(func(i int) {
Printf("%v: %vn", i, s.Index(i).Interface())
})
}
}
func for_each(f func(int)) (i int) {
defer func() {
recover()
}
for ; ; i++ {
f(i)
}
}

108. PROGRAMMINGWITH
OBJECTS

109. PROGRAMMINGWITH
OBJECTS
TYPES + METHODS = OBJECTS

110. TYPES + METHODS = OBJECTS
package main
import . "fmt"
func main() {
s := IterableSlice{ 0, 2, 4, 6, 8 }
i := 0
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
}
type IterableSlice []int
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

111. TYPES + METHODS = OBJECTS
package main
import . "fmt"
func main() {
s := IterableSlice{ 0, 2, 4, 6, 8 }
i := 0
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
}
type IterableSlice []int
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

112. TYPES + METHODS = OBJECTS
package main
import . "fmt"
func main() {
s := IterableSlice{ 0, 2, 4, 6, 8 }
i := 0
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
}
type IterableSlice []int
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

113. TYPES + METHODS = OBJECTS
package main
import . "fmt"
func main() {
s := IterableSlice{ 0, 2, 4, 6, 8 }
i := 0
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
}
type IterableSlice []int
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

114. TYPES + METHODS = OBJECTS
package main
import . "fmt"
func main() {
s := IterableSlice{ 0, 2, 4, 6, 8 }
i := 0
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
}
type IterableSlice []int
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

115. PROGRAMMINGWITH
OBJECTS
INTERFACES = POLYMORPHISM

116. INTERFACES = POLYMORPHISM
package main
import . "fmt"
func main() {
var s Iterable = IterableSlice{ 0, 2, 4, 6, 8 }
i := 0
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
}
type Iterable interface {
Each(func(interface{}))
}
type IterableSlice []int
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

117. INTERFACES = POLYMORPHISM
package main
import . "fmt"
func main() {
var s Iterable = IterableSlice{ 0, 2, 4, 6, 8 }
i := 0
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
}
type Iterable interface {
Each(func(interface{}))
}
type IterableSlice []int
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

118. INTERFACES = POLYMORPHISM
package main
import . "fmt"
func main() {
var s Iterable = IterableSlice{ 0, 2, 4, 6, 8 }
i := 0
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
}
type Iterable interface {
Each(func(interface{}))
}
type IterableSlice []int
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

119. INTERFACES = POLYMORPHISM
package main
import . "fmt"
func main() {
print_values(IterableLimit(5))
print_values(IterableSlice{ 0, 2, 4, 6, 8 })
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableLimit int
type IterableSlice []int
func (i IterableLimit) Each(f func(interface{})) {
for v := IterableLimit(0); v < i; v++ {
f(v)
}
}
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

120. INTERFACES = POLYMORPHISM
package main
import . "fmt"
func main() {
print_values(IterableLimit(5))
print_values(IterableSlice{ 0, 2, 4, 6, 8 })
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableLimit int
type IterableSlice []int
func (i IterableLimit) Each(f func(interface{})) {
for v := IterableLimit(0); v < i; v++ {
f(v)
}
}
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

121. INTERFACES = POLYMORPHISM
package main
import . "fmt"
func main() {
print_values(IterableLimit(5))
print_values(IterableSlice{ 0, 2, 4, 6, 8 })
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableLimit int
type IterableSlice []int
func (i IterableLimit) Each(f func(interface{})) {
for v := IterableLimit(0); v < i; v++ {
f(v)
}
}
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

122. INTERFACES = POLYMORPHISM
package main
import . "fmt"
func main() {
print_values(IterableLimit(5))
print_values(IterableSlice{ 0, 2, 4, 6, 8 })
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableLimit int
type IterableSlice []int
func (i IterableLimit) Each(f func(interface{})) {
for v := IterableLimit(0); v < i; v++ {
f(v)
}
}
func (i IterableSlice) Each(f func(interface{})) {
for _, v := range i {
f(v)
}
}

123. PROGRAMMINGWITH
OBJECTS
IMMUTABILITY IS A CHOICE

124. IMMUTABILITY IS A CHOICE
package main
import . "fmt"
func main() {
s := IterableRange{ 0, 2, 5 }
print_values(s)
print_values(s)
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableRange struct {
start int
step int
limit int
}
func (r IterableRange) Each(f func(interface{})) {
for; r.limit > 0; r.limit-- {
f(r.start)
r.start += r.step
}
}

125. IMMUTABILITY IS A CHOICE
package main
import . "fmt"
func main() {
s := IterableRange{ 0, 2, 5 }
print_values(s)
print_values(s)
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableRange struct {
start int
step int
limit int
}
func (r IterableRange) Each(f func(interface{})) {
for; r.limit > 0; r.limit-- {
f(r.start)
r.start += r.step
}
}

126. IMMUTABILITY IS A CHOICE
package main
import . "fmt"
func main() {
s := IterableRange{ 0, 2, 5 }
print_values(s)
print_values(s)
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableRange struct {
start int
step int
limit int
}
func (r IterableRange) Each(f func(interface{})) {
for; r.limit > 0; r.limit-- {
f(r.start)
r.start += r.step
}
}

127. IMMUTABILITY IS A CHOICE
package main
import . "fmt"
func main() {
s := IterableRange{ 0, 2, 5 }
print_values(s)
print_values(s)
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableRange struct {
start int
step int
limit int
}
func (r IterableRange) Each(f func(interface{})) {
for; r.limit > 0; r.limit-- {
f(r.start)
r.start += r.step
}
}

128. IMMUTABILITY IS A CHOICE
package main
import . "fmt"
func main() {
s := &IterableRange{ 0, 2, 5 }
print_values(s)
print_values(s)
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableRange struct {
start int
step int
limit int
}
func (r IterableRange) Each(f func(interface{})) {
for; r.limit > 0; r.limit-- {
f(r.start)
r.start += r.step
}
}

129. IMMUTABILITY IS A CHOICE
package main
import . "fmt"
func main() {
s := &IterableRange{ 0, 2, 5 }
print_values(s)
print_values(s)
}
func print_values(s Iterable) (i int) {
s.Each(func(v interface{}) {
Printf("%v: %vn", i, v)
i++
})
return i
}
type Iterable interface {
Each(func(interface{}))
}
type IterableRange struct {
start int
step int
limit int
}
func (r *IterableRange) Each(f func(interface{})) {
for; r.limit > 0; r.limit-- {
f(r.start)
r.start += r.step
}
}

130. OO makes code understandable by
encapsulating moving parts.
FP makes code understandable by
minimizing moving parts.
Michael Feathers
@mfeathers
LEANPUB://GONOTEBOOK

131. FUNCTIONSAS
PARADIGM

132. FUNCTIONSAS
PARADIGM
A PURE FUNCTION

133. A PURE FUNCTION
package main
import "os"
func main() {
os.Exit(add(3, 4))
}
func add(x, y int) int {
return x + y
}

134. A PURE FUNCTION
package main
import "os"
func main() {
os.Exit(add(3, 4))
}
func add(x, y int) int {
return x + y
}

135. A PURE FUNCTION
package main
import "os"
func main() {
os.Exit(add(3, 4))
}
func add(x int, y int) int {
return x + y
}

136. A PURE FUNCTION
package main
import "os"
func main() {
os.Exit(add(3, 4))
}
func add(x int, y int) int {
return x + y
}

137. A PURE FUNCTION
package main
import "os"
func main() {
os.Exit(add(3, 4))
}
func add(x int, y int) int {
return x + y
}

138. A PURE FUNCTION
package main
import "os"
import "strconv"
func main() {
x, _ := strconv.Atoi(os.Args[1])
y, _ := strconv.Atoi(os.Args[2])
os.Exit(add(x, y))
}
func add(x, y int) int {
return x + y
}

139. A PURE FUNCTION
package main
import "os"
import "strconv"
func main() {
x, _ := strconv.Atoi(os.Args[1])
y, _ := strconv.Atoi(os.Args[2])
os.Exit(add(x, y))
}
func add(x, y int) int {
return x + y
}

140. A PURE FUNCTION
package main
import "os"
import "strconv"
func main() {
x, _ := strconv.Atoi(os.Args[1])
y, _ := strconv.Atoi(os.Args[2])
os.Exit(add(x, y))
}
func add(x, y int) int {
return x + y
}

141. A PURE FUNCTION
package main
import "os"
import "strconv"
func main() {
os.Exit(add(arg(0), arg(1)))
}
func arg(n int) (r int) {
r, _ = strconv.Atoi(os.Args[n + 1])
return
}
func add(x, y int) int {
return x + y
}

142. A PURE FUNCTION
package main
import "os"
import "strconv"
func main() {
var sum int
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
sum = add(sum, x)
}
os.Exit(sum)
}
func add(x, y int) int {
return x + y
}

143. A PURE FUNCTION
package main
import "os"
import "strconv"
func main() {
var sum int
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
sum = add(sum, x)
}
os.Exit(sum)
}
func add(x, y int) int {
return x + y
}

144. FUNCTIONSAS
PARADIGM
BEING IMPURE

145. BEING IMPURE
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
accumulate(x)
}
os.Exit(y)
}
var y int
func accumulate(x int) {
y += x
}

146. BEING IMPURE
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
accumulate(x)
}
os.Exit(y)
}
var y int
func accumulate(x int) {
y += x
}

147. BEING IMPURE
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
accumulate(x)
}
os.Exit(y)
}
var y int
func accumulate(x int) {
y += x
}

148. BEING IMPURE
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
accumulate(x)
}
os.Exit(y)
}
var y int
func accumulate(x int) {
y += x
}

149. BEING IMPURE
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a.Add(x)
}
os.Exit(int(a))
}
var a Accumulator
type Accumulator int
func (a *Accumulator) Add(y int) {
*a += Accumulator(y)
}

150. BEING IMPURE
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a.Add(x)
}
os.Exit(int(a))
}
var a Accumulator
type Accumulator int
func (a *Accumulator) Add(y int) {
*a += Accumulator(y)
}

151. BEING IMPURE
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a.Add(x)
}
os.Exit(int(a))
}
var a Accumulator
type Accumulator int
func (a *Accumulator) Add(y int) {
*a += Accumulator(y)
}

152. BEING IMPURE
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a.Add(x)
}
os.Exit(int(a))
}
var a Accumulator
type Accumulator int
func (a Accumulator) Add(y int) {
a += Accumulator(y)
}

153. FUNCTIONSAS
PARADIGM
FUNCTIONS WITH MEMORY

154. FUNCTIONS WITH MEMORY
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a(0))
}
var a = MakeAccumulator()
func MakeAccumulator() func(int) int {
var y int
return func(x int) int {
y += x
return y
}
}

155. FUNCTIONS WITH MEMORY
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a(0))
}
var a = MakeAccumulator()
func MakeAccumulator() func(int) int {
var y int
return func(x int) int {
y += x
return y
}
}

156. FUNCTIONS WITH MEMORY
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a(0))
}
var a = MakeAccumulator()
func MakeAccumulator() func(int) int {
var y int
return func(x int) int {
y += x
return y
}
}

157. FUNCTIONS WITH MEMORY
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a(0))
}
var a = MakeAccumulator()
func MakeAccumulator() func(int) int {
var y int
return func(x int) int {
y += x
return y
}
}

158. FUNCTIONS WITH MEMORY
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a(0))
}
var a = MakeAccumulator()
func MakeAccumulator() func(int) int {
var y int
return func(x int) int {
y += x
return y
}
}

159. FUNCTIONS WITH MEMORY
package main
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a(0))
}
var a = MakeAccumulator()
type Accumulator func(int) int
func MakeAccumulator() Accumulator {
var y int
return func(x int) int {
y += x
return y
}
}

160. FUNCTIONS WITH MEMORY
package main
import "os"
import "strconv"
func main() {
a := MakeAccumulator()
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a(0))
}
type Accumulator func(int) int
func MakeAccumulator() Accumulator {
var y int
return func(x int) int {
y += x
return y
}
}

161. FUNCTIONS WITH MEMORY
package main
import "os"
import "strconv"
func main() {
a := MakeAccumulator()
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a(0))
}
func MakeAccumulator() func(int) int {
var y int
return func(x int) int {
y += x
return y
}
}

162. FUNCTIONSAS
PARADIGM
FUNCTIONS AS OBJECTS

163. FUNCTIONS AS OBJECTS
package main
import "os"
import "strconv"
func main() {
a := MakeAccumulator()
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a.Int())
}
type Accumulator func(int) int
func MakeAccumulator() Accumulator {
var y int
return func(x int) int {
y += x
return y
}
}
func (a Accumulator) Int() int {
return a(0)
}

164. FUNCTIONS AS OBJECTS
package main
import "os"
import "strconv"
func main() {
a := MakeAccumulator()
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a(x)
}
os.Exit(a.Int())
}
type Accumulator func(int) int
func MakeAccumulator() Accumulator {
var y int
return func(x int) int {
y += x
return y
}
}
func (a Accumulator) Int() int {
return a(0)
}

165. FUNCTIONS AS OBJECTS
package main
import "os"
import "strconv"
func main() {
a := MakeAccumulator()
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a.Add(x)
}
os.Exit(a.Int())
}
type Accumulator func(int) int
func MakeAccumulator() Accumulator {
var y int
return func(x int) int {
y += x
return y
}
}
func (a Accumulator) Int() int {
return a(0)
}
func (a Accumulator) Add(x
interface{}) {
switch x := x.(type) {
case int:
a(x)
case Accumulator:
a(x.Value())
}
}

166. FUNCTIONS AS OBJECTS
package main
import "os"
import "strconv"
func main() {
a := MakeAccumulator()
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a.Add(MakeAccumulator()(x))
}
os.Exit(a.Int())
}
type Accumulator func(int) int
func MakeAccumulator() Accumulator {
var y int
return func(x int) int {
y += x
return y
}
}
func (a Accumulator) Int() int {
return a(0)
}
func (a Accumulator) Add(x
interface{}) {
switch x := x.(type) {
case int:
a(x)
case Accumulator:
a(x.Value())
}
}

167. FUNCTIONS AS OBJECTS
package main
import "os"
import "strconv"
func main() {
a := MakeAccumulator()
for _, v := range os.Args[1:] {
x, _ := strconv.Atoi(v)
a.Add(MakeAccumulator()(x))
}
os.Exit(a.Int())
}
type Accumulator func(int) int
type Integer interface {
Int() int
}
func MakeAccumulator() Accumulator {
var y int
return func(x int) int {
y += x
return y
}
}
func (a Accumulator) Int() int {
return a(0)
}
func (a Accumulator) Add(x interface{}) {
switch x := x.(type) {
case int:
a(x)
case Integer:
a(x.Int())
}
}

168. FUNCTIONSIN
MATHEMATICS

169. COMPUTING FACTORIALS

170. COMPUTING FACTORIALS
0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880

171. FUNCTIONSIN
MATHEMATICS
ITERATING FACTORIALS

172. ITERATING FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = 1
for ; n > 0; n-- {
r *= n
}
}
return
}

173. ITERATING FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = 1
for ; n > 0; n-- {
r *= n
}
}
return
}

174. ITERATING FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = 1
for ; n > 0; n-- {
r *= n
}
}
return
}

175. ITERATING FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = 1
for ; n > 0; n-- {
r *= n
}
}
return
}

176. ITERATING FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = 1
for ; n > 0; n-- {
r *= n
}
}
return
}

177. ITERATING FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = 1
for ; n > 0; n-- {
r *= n
}
}
return
}

178. ITERATING FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) int {
r := 1
switch {
case n < 0:
panic(n)
case n > 0:
for ; n > 0; n-- {
r *= n
}
}
return r
}

179. ITERATING FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

180. ITERATING FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

181. FUNCTIONSIN
MATHEMATICS
MULTIPLE FACTORIALS

182. MULTIPLE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
for _, v := range os.Args[1:] {
if x, e := strconv.Atoi(v); e != nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

183. MULTIPLE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
for _, v := range os.Args[1:] {
if x, e := strconv.Atoi(v); e != nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

184. MULTIPLE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
for _, v := range os.Args[1:] {
if x, e := strconv.Atoi(v); e == nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

185. MULTIPLE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
for _, v := range os.Args[1:] {
if x, e := strconv.Atoi(v); e == nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

186. MULTIPLE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
for _, v := range os.Args[1:] {
if x, e := strconv.Atoi(v); e == nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

187. MULTIPLE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
for _, v := range os.Args[1:] {
if x, e := strconv.Atoi(v); e == nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

188. MULTIPLE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
if x, e := strconv.Atoi(v); e == nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

189. FUNCTIONSIN
MATHEMATICS
HIGHER ORDER FUNCTIONS

190. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
func() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
if x, e := strconv.Atoi(v); e == nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}()
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

191. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
func() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
if x, e := strconv.Atoi(v); e == nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}()
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

192. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
func() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
if x, e := strconv.Atoi(v); e == nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}()
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

193. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
func() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
if x, e := strconv.Atoi(v); e == nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}()
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

194. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
SafeExecute(func(i int) {
Printf("%v!: %vn", i, Factorial(i))
})(v)
}
}
func SafeExecute(f func(int)) func(string) {
return func(v string) {
defer func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}()
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

195. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
SafeExecute(func(i int) {
Printf("%v!: %vn", i, Factorial(i))
})(v)
}
}
func SafeExecute(f func(int)) func(string) {
return func(v string) {
defer func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}()
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

196. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
SafeExecute(func(i int) {
Printf("%v!: %vn", i, Factorial(i))
})(v)
}
}
func SafeExecute(f func(int)) func(string) {
return func(v string) {
defer func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}()
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

197. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
SafeExecute(func(i int) {
Printf("%v!: %vn", i, Factorial(i))
})(v)
}
}
func SafeExecute(f func(int)) func(string) {
return func(v string) {
defer func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}()
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

198. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
var errors int
f := func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}
for _, v := range os.Args[1:] {
if !SafeExecute(f)(v) {
errors++
}
}
os.Exit(errors)
}
func SafeExecute(f func(int)) func(string) bool {
return func(v string) (r bool) {
defer func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
s}
}()
if x, e := strconv.Atoi(v); e == nil {
f(x)
r = true
} else {
panic(v)
}
return
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

199. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
var errors int
f := func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}
for _, v := range os.Args[1:] {
if !SafeExecute(f)(v) {
errors++
}
}
os.Exit(errors)
}
func SafeExecute(f func(int)) func(string) bool {
return func(v string) (r bool) {
defer func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}()
if x, e := strconv.Atoi(v); e == nil {
f(x)
r = true
} else {
panic(v)
}
return
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

200. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
var errors int
f := func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}
for _, v := range os.Args[1:] {
if !SafeExecute(f)(v) {
errors++
}
}
os.Exit(errors)
}
func SafeExecute(f func(int)) func(string) bool {
return func(v string) (r bool) {
defer func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}()
if x, e := strconv.Atoi(v); e == nil {
f(x)
r = true
} else {
panic(v)
}
return
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

201. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
var errors int
f := func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}
for _, v := range os.Args[1:] {
if !SafeExecute(f)(v) {
errors++
}
}
os.Exit(errors)
}
func SafeExecute(f func(int)) func(string) bool {
return func(v string) (r bool) {
defer func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}()
if x, e := strconv.Atoi(v); e == nil {
f(x)
r = true
} else {
panic(v)
}
return
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

202. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
var errors int
for _, v := range os.Args[1:] {
SafeExecute(
func(i int) {
Printf("%v!: %vn", i, Factorial(i))
},
func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
errors++
}
},
)(v)
}
os.Exit(errors)
}
func SafeExecute(f func(int), e func()) func(string) {
return func(v string) {
defer e()
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

203. HIGHER ORDER FUNCTIONS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
var errors int
for _, v := range os.Args[1:] {
SafeExecute(
func(i int) {
Printf("%v!: %vn", i, Factorial(i))
},
func() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
errors++
}
},
)(v)
}
os.Exit(errors)
}
func SafeExecute(f func(int), e func()) func(string) {
return func(v string) {
defer e()
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

204. FUNCTIONSIN
MATHEMATICS
CURRYING

205. CURRYING

206. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanicFor(UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}), PrintErrorMessage)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanicFor(f, e func()) {
defer e()
f()
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

207. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanicFor(UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}), PrintErrorMessage)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanicFor(f, e func()) {
defer e()
f()
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

208. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanicFor(UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}), PrintErrorMessage)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanicFor(f, e func()) {
defer e()
f()
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

209. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanicFor(UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}), PrintErrorMessage)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanicFor(f, e func()) {
defer e()
f()
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

210. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanicFor(UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}), PrintErrorMessage)()
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanicFor(f, e func()) func() {
return func() {
defer e()
f()
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

211. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanicFor(UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}), PrintErrorMessage)()
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanicFor(f, e func()) func() {
return func() {
defer e()
f()
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

212. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

213. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

214. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

215. CURRYING
package main
import . "fmt"
import "os"
import "strconv"
func main() {
p := OnPanic(PrintErrorMessage)
for _, v := range os.Args[1:] {
p(UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
if n < 0 {
panic(n)
}
for r = 1; n > 0; n-- {
r *= n
}
return
}

216. FUNCTIONSIN
MATHEMATICS
RECURSION

217. RECURSION
package main
func main() {
main()
}

218. RECURSION
package main
func main() {
main()
}

219. RECURSION
package main
func main() {
main()
}

220. RECURSION
package main
func main() {
defer func() {
recover()
}
main()
}

221. RECURSION
package main
import "os"
import"strconv"
var limit int
func init() {
if x, e := strconv.Atoi(os.Args[1]); e == nil {
limit = x
}
}
func main() {
limit--
if limit > 0 {
main()
}
}

222. RECURSION
package main
import "os"
import"strconv"
var limit int
func init() {
if x, e := strconv.Atoi(os.Args[1]); e == nil {
limit = x
}
}
func main() {
limit--
if limit > 0 {
main()
}
}

223. RECURSION
package main
import "os"
import"strconv"
var limit int
func init() {
if x, e := strconv.Atoi(os.Args[1]); e == nil {
limit = x
}
}
func main() {
limit--
if limit > 0 {
main()
}
}

224. RECURSION
package main
import "os"
import"strconv"
var limit int
func init() {
if x, e := strconv.Atoi(os.Args[1]); e == nil {
limit = x
}
}
func main() {
limit--
if limit > 0 {
main()
}
}

225. FUNCTIONSIN
MATHEMATICS
RECURSIVE FACTORIALS

226. RECURSIVE FACTORIALS

227. RECURSIVE FACTORIALS

228. RECURSIVE FACTORIALS

229. RECURSIVE FACTORIALS

230. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = 1
for ; n > 0; n-- {
r *= n
}
}
return
}

231. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = 1
for ; n > 0; n-- {
r *= n
}
}
return
}

232. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = 1
for ; n > 0; n-- {
r *= n
}
}
return
}

233. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
x, _ := strconv.Atoi(os.Args[1])
Printf("%v!: %vn", x, Factorial(x))
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

234. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
defer func() {
if x := recover(); x != nil {
Println("no factorial")
}
}()
for _, v := range os.Args[1:] {
if x, e := strconv.Atoi(v); e != nil {
Printf("%v!: %vn", x, Factorial(x))
} else {
panic(v)
}
}
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

235. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
for _, v := range os.Args[1:] {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

236. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func Each(s []string, f func(string)) {
for _, v := range s {
f(v)
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

237. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func Each(s []string, f func(string)) {
for _, v := range s {
f(v)
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

238. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func Each(s []string, f func(string)) {
for _, v := range s {
f(v)
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

239. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

240. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

241. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

242. RECURSIVE FACTORIALS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func Factorial(n int) (r int) {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
return
}

243. FUNCTIONSIN
MATHEMATICS
CACHING RESULTS

244. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
var cache map[int] int = make(map[int] int)
func Factorial(n int) (r int) {
if r = cache[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
cache[n] = r
}
return
}

245. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
var cache map[int] int = make(map[int] int)
func Factorial(n int) (r int) {
if r = cache[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
cache[n] = r
}
return
}

246. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
var cache map[int] int = make(map[int] int)
func Factorial(n int) (r int) {
if r = cache[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
cache[n] = r
}
return
}

247. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
var cache map[int] int = make(map[int] int)
func Factorial(n int) (r int) {
if r = cache[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
cache[n] = r
}
return
}

248. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, Factorial(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
var cache map[int] int = make(map[int] int)
func Factorial(n int) (r int) {
if r = cache[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * Factorial(n - 1)
}
cache[n] = r
}
return
}

249. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
c := make(Cache)
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, c.Factorial(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
type Cache map[int] int
func (c Cache) Factorial(n int) (r int) {
if r = c[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * c.Factorial(n - 1)
}
c[n] = r
}
return
}

250. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
c := make(Cache)
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, c.Factorial(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
type Cache map[int] int
func (c Cache) Factorial(n int) (r int) {
if r = c[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * c.Factorial(n - 1)
}
c[n] = r
}
return
}

251. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
f := MakeFactorial()
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, f(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func MakeFactorial() (f func(int) int) {
c := make(map[int] int)
return func(n int) (r int) {
if r = c[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * f(n - 1)
}
c[n] = r
}
return
}
}

252. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
f := MakeFactorial()
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, f(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func MakeFactorial() (f func(int) int) {
c := make(map[int] int)
return func(n int) (r int) {
if r = c[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * f(n - 1)
}
c[n] = r
}
return
}
}

253. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
f := MakeFactorial()
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, f(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func MakeFactorial() (f func(int) int) {
c := make(map[int] int)
return func(n int) (r int) {
if r = c[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * f(n - 1)
}
c[n] = r
}
return
}
}

254. CACHING RESULTS
package main
import . "fmt"
import "os"
import "strconv"
func main() {
f := MakeFactorial()
Each(os.Args[1:], func(v string) {
OnPanic(PrintErrorMessage)(
UseNumericParam(v, func(i int) {
Printf("%v!: %vn", i, f(i))
}))
})
}
func PrintErrorMessage() {
if x := recover(); x != nil {
Printf("no defined value for %vn", x)
}
}
func UseNumericParam(v string, f func(i int)) func() {
return func() {
if x, e := strconv.Atoi(v); e == nil {
f(x)
} else {
panic(v)
}
}
}
func Each(s []string, f func(string)) {
if len(s) > 0 {
f(s[0])
Each(s[1:], f)
}
}
func OnPanic(e func()) func(func()) {
return func(f func()) {
defer e()
f()
}
}
func MakeFactorial() (f func(int) int) {
c := make(map[int] int)
return func(n int) (r int) {
if r = c[n]; r == 0 {
switch {
case n < 0:
panic(n)
case n == 0:
r = 1
default:
r = n * f(n - 1)
}
c[n] = r
}
return
}
}