[Haskell-cafe] Lambda and closures in PHP -- could someone please comment?

Richard A. O'Keefe ok at cs.otago.ac.nz
Sun Jun 22 22:23:26 EDT 2008

This is increasingly less relevant to Haskell, except
of course to demonstrate what a nice language Haskell is.
On 20 Jun 2008, at 11:34 pm, Jules Bean wrote:
> I think where I differ on you is how to map the semantics of a C- 
> like language to explicit references.
> I would argue that the glyph "c" in a C-like language denotes the  
> value of C, not the reference to it. C-like languages have, for the  
> most part, value semantics, and call-by-value.
> The exception of course is what C-like languages called "lvalues",  
> but lvalues are only really on the left of the = sign and a few  
> other special positions. I think that's the exception and not the  
> rule.

No, this is back to front.  C basically follows the Algol 68 idea that
the lvalue is the normative thing, and that there is an IMPLICIT  
from a variable to its value in certain contexts.  C is full of implicit
coercions: perhaps the most famous is the one that says that in almost  
contexts an array is quietly coerced to a pointer to its first element.

The key observation is that an implicit coercion from a variable to its
contents is possible, whereas an implicit coercion from a value to "the"
variable that holds it is not.   Only the "a variable really stands for
its address" view is coherent.

> In C, of course, if you want to capture the reference you do it  
> explicitly with "&c".

If we can use evidence from a relative to probe such questions,
the fact that you *don't* need an explicit "&" in C++ (when you find a  
to a variable, you use "c", not "&c") strongly suggests that the  
"variable stands
for location" view is the more useful one.

Thankfully, Haskell saves us these perplexities.
(And replaces them with other perplexities...)

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