Re: [Haskell-cafe] ANN: HLint 1.2

On Jan 12, 2009, at 12:47 PM, Max Bolingbroke wrote:

2009/1/12 Jan-Willem Maessen :

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On Jan 12, 2009, at 9:01 AM, Duncan Coutts wrote:

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No because the current definition are recursive and ghc cannot inline recursive functions.

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Then the map can be inlined at the call site and the 'f' inlined into the body of 'go'.

This seems like exactly the sort of mechanical transformation that computers do quickly and accurately, and humans get wrong. Surely it wouldn't be that hard for GHC to transform self recursion in this way (possibly subject to the condition that the result be worth inlining)?

GHC should indeed be doing so. I'm working (on and off) to work out some suitable heuristics and put the transformation into ghc -O2. There are a few wrinkles that still need sorting out, but preliminary indications are that it decreases the runtime of our standard benchmark suite, nofib, by 12% or so.

This is excellent news, quite apart from Don's observation that it isn't particularly relevant for map (where we are essentially using RULES to instantiate an alternative definition in terms of foldr/ build, if I understand his message rightly). Self recursion is abut so much more than map! -Jan

Cheers, Max