🚀 go-pugleaf

In article <9104262016.AA28063@enuxha.eas.asu.edu> surendar@ENUXHA.EAS.ASU.EDU (Surendar Chandra) writes:
> > val a = 1;
> > a ;
> | 1 : int ;
> > fun b c = c * a ;
> > b 2 ;
> | 2 : int ;
> > val a = 3;
> > b 2 ;
> | 2 : int ;
> ^^^^^^^^ Why does it do it like this.. Why doesn't it look up at the current
> value of the variable 'a'. Why does it store the current value of 'a' in the
> function during compilation itself? WHat is the logic behind this? I could
> not lay my hands on a good reference for SML and most of the books don't seem
> to talk about this at all.

ML is a 'real', i.e. 'single-assignment' language. Once a variable is defined,
it cannot change its value. So, when you define a=1, then a=3, the second
time you create a new variable hiding the old one. So, ML not being
dynamically scoped, the function b has as its closure the environment at
the time of its creation, i.e. seeing only the 'old' a.
You need not think that that value of a is compiled into the function b
(although this could be done); its simply a consequence of not being able
to alter something once its created.

Hope that helps,

Markus



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