AST/Type Specialization

[andrew-johnson-4]

This is the logical opposite of a macro

for x in y { z }

can be inefficient due to the iter -> Maybe<item> signature of the iterator. This leads to unnecessary creation of an intermediate Maybe object which can be quite expensive compared to a normal for loop. To fix this, some sort of AST transformation is necessary, but how should this be structured?

There could be some type of type directed rewrite rule here to optimize the AST in place.

let iter = y;
let continue-iter = true;
while continue-iter match &iter.next {
   Some(x) => z;
   None => continue-iter = false;
}

would be replaced with

let iter = y;
while non-zero(iter) match iter {
   LCons(x,rest) => (z; iter = rest;);
}

for lists. This operation needs to be aware of AST patterns or understand them enough to do transformations. This is a specialization from iter to List<_> for the for macro, however it can't really be done during preprocessing and should also be generalized for code patterns that don't use a macro.