This document provides an introduction and overview of Io, an open-source object-oriented programming language with a classless design based on prototypes. Some key points covered include: - Io is object-oriented, classless, and uses prototype-based inheritance. Objects receive and respond to messages. - Operators are implemented as methods, and concurrency is supported through lightweight coroutines. - Conditionals, loops, and other control structures are implemented using messages rather than special syntax. - Metaprogramming allows messages and the abstract syntax tree to be modified at runtime, enabling powerful dynamic programming capabilities.

1. Intro to Io
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2. Intro to Io
* Not really an Intro
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3. Me
• Jeremy Tregunna
• iOS & Mac developer
• Aspiring hardware designer (FPGAs, etc)
• Twitter: @jtregunna
• App.net: @jtregunna
• GitHub: @jeremytregunna
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4. Slideshare
• Small fonts, check this out to follow along better:
http://www.slideshare.net/jtregunna/intro-to-io
Github
• Code!
https://github.com/jeremytregunna/intro-to-io
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5. What is it?
• Object-oriented
• Classless design (based on Prototypes)
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6. What is it?
• Object-oriented
• Classless design (based on Prototypes)
1 Elephant := Object clone do(
2 earSize := “medium”
3 height := “big”
4 color := Color greyColor
5 )
6
7 Dumbo := Elephant clone do(
8 earSize = “large”
9 canFly := true
10 height := “short”
11 wearsBowtie := true
12 )
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7. What is it?
• Object-oriented
• Classless design (based on Prototypes)
1 Elephant := Object clone do(
2 earSize := “medium”
3 height := “big”
4 color := Color greyColor
5 )
6
7 Dumbo := Elephant clone do(
8 earSize = “large”
9 canFly := true
10 height := “short”
11 wearsBowtie := true
12 )
• Open Source
• Magical tool belt
• Slow
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8. Fundamentals
• Objects receive messages
• Messages are first class entities
1 msg := message(+ 2 * 5)
2 1 doMessage(msg) == 11 # same as: 1 + 2 * 5
• Objects are unavoidable
Every message send is received by some object, 100% of the time.
• Operators are implemented as methods
1 1 + 2 * 5 # is really: 1 +(2) *(5)
2 foo := 42 # is really: setSlot(“foo”, 42)
• Concurrency first class
Cooperative threading
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9. Operators
• Operators are messages, they have a precedence.
• Precedence is defined in the OperatorTable
• Two types of operators, binary and assignment.
1 /* Binary */ 1 + 2
2 /* Assign */ foo := 42
• You can define your own
1 # operators.io
2 OperatorTable addOperator("blah", 14)
3 blah := method(x, "#{x}#{x}" interpolate println)
4 doFile("opertest.io")
1 # opertest.io
2 message(blah "bar") println
3 blah "bar"
• All operators must be defined before the parser
parses code that uses them!!!
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10. Conditionals
• If statement isn’t a statement
1 if := method(c,
2 (c != nil and c != false) ifTrue(return call evalArgAt(1)) ifFalse(return call evalArgAt(2))
3 )
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11. Conditionals
• If statement isn’t a statement
1 if := method(c,
2 (c != nil and c != false) ifTrue(return call evalArgAt(1)) ifFalse(return call evalArgAt(2))
3 )
• Only needs one primitive to implement.
1 # Using “evalArgAt()” we can selectively evaluate an arbitrary argument
2 true ifTrue := method(call evalArgAt(0); self)
3 true ifFalse := true
4 false ifTrue := false
5 false ifFalse := method(call evalArgAt(0); self)
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12. Conditionals
• If statement isn’t a statement
1 if := method(c,
2 (c != nil and c != false) ifTrue(return call evalArgAt(1)) ifFalse(return call evalArgAt(2))
3 )
• Only needs one primitive to implement.
1 # Using “evalArgAt()” we can selectively evaluate an arbitrary argument
2 true ifTrue := method(call evalArgAt(0); self)
3 true ifFalse := true
4 false ifTrue := false
5 false ifFalse := method(call evalArgAt(0); self)
• Full if() support?
1 if := method(c,
2 call argAt(1) isNil ifTrue(return (c != nil and c != false)) # if() then() ... form
3 (c != nil and c != false) ifTrue(return call evalArgAt(1)) ifFalse(return call evalArgAt(2))
4 )
5 Object then := nil
6 Object else := nil
7 true then := method(call evalArgAt(0); self)
8 true else := true
9 false then := false
10 false else := method(call evalArgAt(0); self)
• Looks familiar...
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13. Metaprogramming
• Here be dragons!
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14. Metaprogramming
• Here be dragons!
• Higher order messaging
• Messages are our AST
• Messages are mutable at runtime
1 Number add := method(n, self + n)
2 5 add(2) == 7
3 Number sub := Number getSlot(“add”) do(message next setName(“-”))
4 5 sub(2) == 3
5 5 add(2) == 3 # ???
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15. Metaprogramming
• Here be dragons!
• Higher order messaging
• Messages are our AST
• Messages are mutable at runtime
1 Number add := method(n, self + n)
2 5 add(2) == 7
3 Number sub := Number getSlot(“add”) do(message next setName(“-”))
4 5 sub(2) == 3
5 5 add(2) == 3 # ???
• Don’t forget to clone
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16. Metaprogramming
• Here be dragons!
• Higher order messaging
• Messages are our AST
• Messages are mutable at runtime
1 Number add := method(n, self + n)
2 5 add(2) == 7
3 Number sub := Number getSlot(“add”) do(message next setName(“-”))
4 5 sub(2) == 3
5 5 add(2) == 3 # ???
• Don’t forget to clone
1 Number sub := Number getSlot(“add”) clone do(message next setName(“-”))
2 5 sub(2) == 3
3 5 add(2) == 7
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17. Concurrency
• Lightweight threading (coroutines)
• Independent of the C Stack*
• Cooperative scheduling of coroutines
* - For pure Io code only.
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18. Concurrency
greeter := Object clone do(
newSlot("coro"); newSlot("waitingCoro")
run := method(
coro = coroDo(
pause
names := list("Fred", "Wilma", "Betty", "Barney")
names foreach(i, name,
if(i == names size - 1,
"#{name}" interpolate println
System exit
,
"#{name}, " interpolate print
)
waitingCoro resume
)
)
)
hello := method(
"Hello " print
setWaitingCoro := Coroutine currentCoro
coro resume
)
)
greeter run; greeter hello
# Hello Fred, Wilma, Betty, Barney
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