Thomas Davie
Hat/MySet.hs:636:60: Couldn't match `Hat.Hat.R (Hat.Hat.List a)' against `Hat.Hat.RefExp' Expected type: Hat.Hat.R (Hat.Hat.Fun a b2) -> Hat.Hat.RefExp -> Hat.Hat.R (Hat.Hat.Fun b1 (Hat.Hat.List b)) Inferred type: Hat.Hat.R (Hat.Hat.Fun a b2) -> Hat.Hat.R (Hat.Hat.List a) -> Hat.Hat.RefExp -> Hat.Hat.R (Hat.Hat.List b2) In the fifth argument of `Hat.Hat.app1', namely `Hat.PreludeBasic.hmap' In the fourth argument of `Hat.Hat.ap2', namely `(Hat.Hat.app1 p391v20v391v29 p391v20v391v27 p Hat.PreludeBasic.amap Hat.PreludeBasic.hmap ff)'
Simplifying, this means it was expecting to be given a function R (a->b) -> R (c->[d]) but was actually supplied with hmap of type R (a->b) -> R [a] -> R [b] Now clearly the latter looks more or less correct for map, whilst the former does not. For one thing, it has too few arguments. Judging by the name, 'hmap' is the worker part of the worker/wrapper split in the traced map. So the fault would appear to be that hat-trans is doing an optimisation incorrectly. It has called the worker function directly, believing the call to be saturated, when in fact it is only partially applied, and it should have called the wrapper instead. Hence the differing arities in the error message. Olaf is the person who will be able to confirm whether this is a correct diagnosis, and if so, to provide the solution. Regards, Malcolm