RULES for Class ops don't fire in HEAD (#4397) · Issues · Glasgow Haskell Compiler / GHC

RULES for Class ops don't fire in HEAD

For the attached programme, compiled with 7.1.20101010, the rule truncate/Double->Int doesn't fire, resulting in

-248407781
1
const 0    took   0.004000s
-248407781
truncate   took   0.940059s
-248407781
double2Int took   0.032002s

i.e. truncate is not rewritten to double2Int, although it is given an explicit type signature (same behaviour without a type signature).

-ddump-rule-firings lists

Rule fired: Class op truncate

among (if I haven't miscounted) 41 Class op xxx rules.

That behaviour keeps the fix for #2271 (closed) from working and is a severe regression for #1434 (closed) .

IMO it's a show-stopper.

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