Commit 2e1b8326 authored by's avatar
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parent 42400001
......@@ -457,6 +457,29 @@ can be used in Stream states and (c) some types are fixed by the user
(e.g., the accumulator here) but we still want to specialise as much
as possible.
Alternatives to ForceSpecConstr
Instead of giving the loop an extra argument of type SPEC, we
also considered *wrapping* arguments in SPEC, thus
data SPEC a = SPEC a | SPEC2
loop = \arg -> case arg of
SPEC state ->
case state of (x,y) -> ... loop (SPEC (x',y')) ...
S2 -> error ...
The idea is that a SPEC argument says "specialise this argument
regardless of whether the function case-analyses it. But this
doesn't work well:
* SPEC must still be a sum type, else the strictness analyser
eliminates it
* But that means that 'loop' won't be strict in its real payload
This loss of strictness in turn screws up specialisation, because
we may end up with calls like
loop (SPEC (case z of (p,q) -> (q,p)))
Without the SPEC, if 'loop' was strict, the case would move out
and we'd see loop applied to a pair. But if 'loop' isn' strict
this doesn't look like a specialisable call.
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