Strict foldl

Marcin 'Qrczak' Kowalczyk qrczak at
Mon Feb 6 14:43:46 EST 2006

Haskell standard should get a strict foldl: either under some new
standard name (foldl' is most common), or just replacing foldl.

Is there a real-life case where a lazy foldl is desirable? I don't
mean a constructed artificial example, I know they exist, but
something which is really used.

Currently usages of foldl fall into two major groups: those which are
inlined and transformed into a strict foldl by an optimizing compiler,
and those which have a space leak and a potential for stack overflow
for large data.

Even if there are cases where a lazy foldl is essential, I would
prefer to have to code them with an explicit recursion, and reserve
foldl for the more common cases where it should better be strict.

   __("<         Marcin Kowalczyk
   \__/       qrczak at

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