On Wed, Mar 31, 2010 at 11:06 AM, Paul Brauner wrote:

data Term = Lam Term | App Term Term | Var Int

instance NFData where  rnf (Lam t)     = rnf t  rnf (App t1 t2) = rnf t1 `seq` rnf t2  rnf (Var x)     = rnf x

the actual datatype doesn't have fancy stuff like higher-order types for constructors, it's really similar. The only difference is that it is a GADT, but this souldn't change anything right?

Did I make some mistake in instancing NFData ?

No, your NFData instance is correct. You first pattern match on the term followed by recursively calling rnf on the sub-terms. This will correctly force the entire term. Maybe you could try using criterion[1] for your benchmark and see if that makes any difference. Something like: {-# LANGUAGE BangPatterns #-} import Criterion.Main main :: IO () main = let !t = genterm in defaultMain [bench "subst" $ nf (subst u) t] regards, Bas [1] http://hackage.haskell.org/package/criterion

Thank you, I will look at that. But it seems that criterion uses NFData no? Paul On Wed, Mar 31, 2010 at 12:57:20PM +0200, Bas van Dijk wrote:

On Wed, Mar 31, 2010 at 11:06 AM, Paul Brauner wrote:

...

data Term = Lam Term | App Term Term | Var Int

instance NFData where  rnf (Lam t)     = rnf t  rnf (App t1 t2) = rnf t1 `seq` rnf t2  rnf (Var x)     = rnf x

the actual datatype doesn't have fancy stuff like higher-order types for constructors, it's really similar. The only difference is that it is a GADT, but this souldn't change anything right?

Did I make some mistake in instancing NFData ?

No, your NFData instance is correct. You first pattern match on the term followed by recursively calling rnf on the sub-terms. This will correctly force the entire term.

Maybe you could try using criterion[1] for your benchmark and see if that makes any difference. Something like:

{-# LANGUAGE BangPatterns #-}

import Criterion.Main

main :: IO () main = let !t = genterm in defaultMain [bench "subst" $ nf (subst u) t]

regards,

Bas

[1] http://hackage.haskell.org/package/criterion

Ok, thank you for all your answers. I'm going to use NFData as advised by everyone. Paul On Wed, Mar 31, 2010 at 10:38:50AM -0700, Bryan O'Sullivan wrote:

On Wed, Mar 31, 2010 at 4:12 AM, Paul Brauner wrote:

...

Thank you, I will look at that. But it seems that criterion uses NFData no?

I do not know of anything wrong with NFData. What you're seeing is much more likely to be a bug in either the benchmarking library you're using, or in your use of it. Most of the benchmarking frameworks on Hackage are extremely dodgy, which was why I wrote criterion.