5 Apr
2001
5 Apr
'01
9:48 a.m.
In that case you need an existential type (not Haskell 98), which GHC and Hugs support thus:
data Row a = forall f. Formula f => Row (f a, Weight)
And incidentally, nhc98 also supports this particular extension with this syntax. (Hbc supports it too, but with a slightly different syntax.) Regards, Malcolm