A crash course in functional programming concepts using Go. Heavy on code, light on theory. You can find the examples at https://github.com/feyeleanor/intro_to_fp_in_go

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
}
}