Let's Talk About Lambda Functions!

[Ian Bicking]

On Wed, 2002-07-31 at 05:17, James J. Besemer wrote:
> Smalltalk's control structures have no pretension
> whatsoever to be related to lambda (or anything
> else I've ever seen before).  Some examples:
> 
>     count timesRepeat: [ block of code ]
> 
>     [ count <= max ]
>             whileTrue: [ another block ]
> 
>     x < 10
>         ifTrue: [ true block ]
>         ifFalse: [ false block ]

Well, it looks a lot like lambda calculus, because True and False are
two different classes, with definitions like:
----
(True)
ifTrue: block
block value "This evaluates the passed block"

ifFalse: block
"do nothing"

(False)
ifTrue: block
"do nothing"

ifFalse: block
block value
----
This should remind one of true/false in lambda calculus (though
obviously with a very different notation).

But, at least in Squeak (and my impression is this is universal among
Smalltalk environments), ifTrue:/ifFalse: don't actually get passed as
method calls/messages.  The compiler specifically looks for those
methods, and turns them into traditional if statements in the bytecode. 
That is, you can't (usefully) implement ifTrue: in your own custom
class.

  Ian