Io

Io is a prototype based language created by Steve Dekorte in 2002.

Animal := Object clone
Animal slotNames

Animal description := "not a plant"

Mouse := Animal clone
jerry := Mouse clone

Anything that starts with uppercase has a “type” slot. The jerry object doesn’t have this.

Animal type
Mouse type
mouse type

Animal slotNames
Mouse slotNames
jerry favoriteFood := "Cheese"

Mouse slotNames
jerry slotNames

Io calls parent object if a slot doesn’t exist.

jerry description
==> Not a plant
jerry description = "Super mouse"

Methods:

Mouse hello := method("Scampers away" println)
jerry hello := method("Hello yourself" println)

jerry getSlot("hello")
==> method(...)

Get prototype of the object

jerry proto
==> Mouse
Mouse proto
==> Animal

The master namespace is called Lobby.

Basic rules

everything is an object
you send messages to objects
objects are created by cloning prototypes
objects remember their prototype
objects have slots (which are hashes/dicts)
slots can contain other objects or methods
a message returns value in a slot or invokes the method there
if the method is not present, the object passes it to prototype

Lists

ls := list(2, 4, 1, 3)
ls sort
ls sum
ls average
ls pop

Maps

capitals = Map clone
capitals atPut("India", "New Delhi")
capitals keys
capitals values
capitals at("India")

Singletons

true, false, nil are singletons
Everything except false and nil are true

true clone
==> true
false clone
==> false

We can make our own objects singletons

Duck := Object clone
Duck clone := Duck
d1 := Duck clone
d2 := Duck clone
d1 == d2
==> true

Looping

if(cond, "true", "false")
i := 1
while(i <= 5, i println; i = i+1)

for(i, 1, 5, i println)

Operator table

OperatorTable
==> ...

OperatorTable addOperator("xor", 11)
true xor := method(bool, if(bool, false, true))
false xor := method(bool, if(bool, true, false))

Io

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