On 3 Oct 2007, at 1:42 pm, PR Stanley wrote:
When a function is declared in C the argument variable has an
address somewhere in the memory:
int f ( int x ) {
return x * x;
}
Wrong. On the machines I use, x will be passed in registers and will
never ever have an address in memory. In fact, unless I hold the Sun
C compiler back by main force, it will probably open code f() so that
there isn't any f any more, let alone any x. Here's the actual SPARC
code generated for f:
f: retl
mulx %o0,%o0,%o0
No memory, no address.
In C, a function call is rather like entering a new block, declaring
some new variables (which might or might not ever go into memory) and
initialising them to the values of the arguments.
In Haskell, carrying out a function call is rather like creating some
new names and *binding* them to promises to evaluate the arguments
(if they are ever needed) and then returning a promise to evaluate the
body (if it is ever needed). The key point is *binding* names to
(deferred calculations of) values, rather than *initialising*
mutable variables to (fully evaluated) values. How this is done is
entirely up to the compiler.
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