While it's true you can do anything you can do with a for loop with a while loop, I picked for.
I really like the capability that for gives you to keep all the operations controlling the loop - initialisation, incrementing and testing - in one place. In C99 (and Perl) you can declare variables in the for statement, and they will have a scope of precisely the for loop. You'll need an extra block to do that with while. So taking the example above, I assume this is intended to synthesise (updated:) ambrus noted that this is equivalent to:
// UNTESTED
for(int a = 1; a<10; a++)
{
printf("%d\n",a);
}
In fact, you'll need an extra block to get the correct scope:
// UNTESTED
// UPDATED: de-obfuscated
{
int a = 1;
while(a<10)
{
printf("%d\n",a);
a++;
}
}
Which is starting to look rather messy.
Context switch back to Perl here!
Synthesising while and foreach from for seems reasonably intuitive to me on the other hand.
# UNTESTED
for (;EXPR;) BLOCK # leave first and third EXPRs blank to be
# equivalent to while (EXPR) BLOCK
# UNTESTED
for (my @list = LIST, VAR = shift @list; # iterate manually through
@list; # LIST in "for" to be
VAR = shift @list) BLOCK # somewhat like
# foreach VAR (LIST) BLOCK
# without the usual aliasing
OK, the foreach is starting to look a bit funny, but a foreach from while will be worse, and spread into the block, rather than be confined to the statement itself.
One issue is that for doesn't have a continue block, but as I come from C I don't tend to use those. continue blocks also split up code that happens every time round the loop, which puts me off. for's third expression is roughly equivalent I suppose, but stuffing a large continue block there could hardly be called good style.
Recursion is another story but I don't think I could live with it as the only looping mechanism. I'd rather have the reverse issue of synthesising recursion, say with a list of hashes, on the rare occasions I really needed it.
updated in response to ambrus's comments.
Also, note:
perl -MO=Deparse -e "for (;<>;){print}"
while (defined($_ = <ARGV>)) {
print $_;
}
-e syntax OK
the for deparses as a while! |