gistfile1.hs

$> cat > foo.hs
{-# RULES "foo/Integer" foo = intFoo #-}

foo :: Num a => a -> a -> a
foo = (+)

intFoo = (-)

main = (putStrLn . show) ((foo (1::Integer) (1::Integer))::Integer)
$> ghc --make -O -ddump-rules -ddump-simpl-stats foo.hs
[1 of 1] Compiling Main             ( foo.hs, foo.o )

==================== Transformation rules ====================
Local rules
"foo/Integer" ALWAYS
    forall {$dNum :: Num Integer} foo @ Integer $dNum = intFoo

Imported rules



==================== Top-level specialisations ====================



==================== FloatOut stats: ====================
0 Lets floated to top level; 0 Lets floated elsewhere; from 0 Lambda groups



==================== FloatOut stats: ====================
1 Lets floated to top level; 0 Lets floated elsewhere; from 1 Lambda groups



==================== Grand total simplifier statistics ====================
Total ticks:     75

19 PreInlineUnconditionally
22 PostInlineUnconditionally
11 UnfoldingDone
2 LetFloatFromLet
16 BetaReduction
5 KnownBranch
10 SimplifierDone


Linking foo ...
.

$> ./foo
2