I try (not very well) to explain Io, a small language, a la X in Y minutes, as much as I know anyway

This is mostly a recollection from old notes, I wanted to get it all in one place (another place, perhaps).

The real Io tutorial is at least as good, let’s just be clear. This is just a blog.

First, some wordy explainy parts, then below that code just like X in Y minutes.

Io, in words

  1. all values are objects, all actions are messages
  2. objects are prototypes, & classes, & namespaces, & contexts
  3. blocks are functions, & methods, & closures
  4. messages are operators, & calls, & assigns, & accesses
  5. objects are:
    1. lists of slots, which are key/value pairs
    2. list of protos, which are objects from which it inherits
  6. prototype objects, usually Uppercase, have a clone slot
  7. when an object is cloned, its init slot is called
  8. messages will route to the object’s slots, then each of its protos’ slots until a matching slot is found. This is fully dynamic and happens entirely at runtime.
  9. Io has no globals. The toplevel is an object called the Lobby.

  10. Slots can be created by assigning to them.

    Obj slot  :=  value

  11. methods are anonymous functions that take a message for a receiver, create a locals object, and assign the proto & self slot to the receiver.

    method("hello!" print)
  12. methods return their last value by default

  13. methods can take many arguments

    method(a, b, c, d, a*d - b*c)
  14. blocks are basically methods, except their context is lexically-bound not to the receiver/target, but to the context where the block was created
  15. for either blocks/methods, its call slot holds information about the block/method activation: sender, message, target, slotContext, activated
  16. an object can both receive & pass a message with resend. This will forward the same message to a proto.

Io, in plain sight

I haven’t double-checked all of this code, so I apologize if I’ve screwed anything up.

#
# Primitives, literals, declarations, assignments, I/O
#
true
false
nil
1
2.0
1 + 2.0
2 / 3.0
"hello?"
list(1, 2, "3")
                # lists are heterogenous
x := 1
                # x is declared with :=
x = 2
                # x is updated with =
"hello, world!" println
"X = #{x}" interpolate println
                # "X = 2"
square := method(x, x*x)
"#{x}^2 = #{square(x)}" interpolate println
                # "2^2 = 4"
("pine" .. "apple") println
                # "pineapple"
(if(1 < 2, "1", "2") .. " is smaller") println
                # if is an expression

"X is #{x} before the loop" interpolate println
while(x < 5, x = x + 1)
"X is #{x} after the loop" interpolate println

for(i, 1, 10, i print)
                # 12345678910
for(i, 1, 10, 3, i print)
                # 14710

fibonacci := method(n,
    if(n < 2,
        1,
        fibonacci(n - 2) + fibonacci(n - 1)
    )
)

fibonacciIterative := method(n,
    a := 0;
    b := 1;
    for(i, 1, n,
        next := a + b;
        a := b;
        b := next
    );
    b
)

Date cpuSecondsToRun(fibonacci(25)) println
Date cpuSecondsToRun(fibonacciIterative(25)) println


#
# Objects & slots, in more detail
#
Object

Object clone
        # different IDs
Object clone

Object sneeze := method("Achoo!" println)
Object sneeze

Object getSlot("sneeze")
        # get the method, don't invoke it
Object getSlot("sneeze") code
        # ..yeah

Lobby

Lobby slotNames
slotNames

3 slotNames
3 proto
3 proto slotNames

"A string" proto
"A string" protos

#
# Message passing, in more detail
#
Knock := Object clone
Knock whoIsIt     := method(call sender)
Knock whoAmI      := method(call receiver)
Knock whatIsIt    := method(call message name)
Knock whatAboutIt := method(call message arguments)

Knock whoIsIt
Knock whoAmI
Knock whatIsIt
Knock whatAboutIt
Knock whatAboutIt()
Knock whatAboutIt(2, 3, x)

Knock sayX := method(x println)

SpecialContext := Object clone
SpecialContext x := "special"

Knock sayX
SpecialContext Knock sayX
SpecialContext Knock whatAboutIt(2, 3, x)

#
# Some "built-ins", provided you've got the JSON extension :P
#   these probably won't work without it
#
list(1, 2, 3) println
list(1, 2, 3) asJson println
list(3, 1, 2) sort println
list(1, 2, 3) sum println

Config := Object clone
Config version := "1.0"
Config name := "io-language"
Config asJson println

Again I’m not sure 100% of the above even “interprets”, so to speak.

I would really like to expand a bit more, on maps, file/http I/O, coroutines. And fix any mistakes.

Sometimes, I get a segfault running these examples through io, but I’m not really sure if it’s user error or what. I’ll figure it out.