Does Smalltalk have closures?

Question

If it has closures, can I assume that I can use many of strong functional style techniques on there?

Answer 1

Yes, Smalltalk has closures. The following code creates a closure that returns the sum of its two arguments:

sum := [ :a :b | a + b ].

Closures are objects that can be instantiated, passed around and manipulated. To evaluate a closure you send value, value:, value:value:, ...

sum value: 1 value: 2.

Closures are prominently used with collections to iterate, filter, map, ... all values of a collection:

aCollection select: [ :each | each isOdd ].
aCollection inject: 0 into: [ :each :result | each + result ].

Furthermore, they are used for control structures like loops:

[ iterator hasNext ]
    whileTrue: [ iterator next ].
1 to: 10 do: [ :each | ... ].

Also conditionals are implemented using closures:

condition
   ifTrue: [ do this ]
   ifFalse: [ do that ]

Answer 2

Pharo has them:

all VMs have closure support required for latest images

makeAdder := [ :x | [ :y | x + y ]].
add2 := makeAdder value: 2.
add2 value: 3.

Returns 5.

But notice that

makeCounter := [ :init | [ init := init + 1. init ]].

won't work (Cannot store into ->init …), like (for example) in CL:

CL-USER> ((lambda (init) (lambda () (incf init))) 0)
#<COMPILED-LEXICAL-CLOSURE #xC7A495E>
CL-USER> (funcall *)
1
CL-USER> (funcall **)
2
CL-USER> (funcall ***)
3

If I'm not mistaken, this used to work before the new closure compiler was introduced. I'm not sure why it doesn't work with the new compiler.