5/5/05, Stuart Cook <scook0 (AT) gmail (DOT) comwrote:

| Meta-op | is | operates on | to produce |

| [ ] | circumfix | infix | prefix |

| ><< | circumfix | infix | infix |

| = | postfix | infix | infix |

| >| prefix | postfix | postfix |

| << | postfix | prefix | prefix |

I find this table very interesting, in that it shows the fundamental
difference between reduce and the existing meta-ops.

The existing meta-operators alter the semantics of the opoerator, but
don't really change its syntax; a unary operator is still unary, a
binary operator is still binary, and so on. Reduce is irreducibly
(pardon the pun) different, in that it alters the syntax as well as
the semantics.

My suggestion is simple:

multi *reduce(&block, *@list is copy) {
my $r=@list.shift;
while(@list) {
$r = block($r, *@list.shift( :elems(&block.arity - 1) );
}
return $r;
}
macro *reduce ($op, $expr) is parsed( / \[ (<infix_operator>) \]
(<expr>)/ ) {
# Would be reworked to produce a parse tree
return "reduce(&infix:<$op>, $expr)";
}

That would result in the following syntaxes:

reduce { $^a / $^b } @foo;
reduce [/] @foo;

$sum = reduce[+] @array;
$fact = reduce[*] 1$num;
$firsttrue = reduce[||] @args;
$firstdef = reduce[//] @args;
@sumrows := reduce[+] @rows;
@foo[09; reduce[;](@dims); 09]

Clearly we could squabble about the exact bracketing operators to use
(I chose square brackets because I thought they'd be less ambiguous
than parentheses or curlies), but I trust you get the idea.

I agree that reduce is very useful, and I even agree that it should be
in core, but it's not *so* useful that it needs to be invokable
without a keyword. Summing a list, let's face it, is likely to
be the most common use for this't common enough an operation to
need such a compact syntax; I can think of more useful meta-ops, like
one that tags each result with the operands that created it, allowing
junctions to be used for the stuff people currently complain they
can't be.

multi sub *infixmetaop:<[ ]( $lhs, $rhs ) {
return call but operands($lhs, $rhs);
}