2012/1/3 Yucheng Zhang<[email protected]>
(Hopefully being a little more explicit about this can help you
understand where things are going wrong.)
[--snip--]
legSome :: LegGram nt t s -> nt -> Either String ([t], s)
The 'nt' you see above
legSome (LegGram g) ntV =
case Main.lookup ntV g of
Nothing -> Left "No word accepted!"
Just l -> let sg = legSome (LegGram (Main.delete ntV g))
subsome :: [RRule nt t s] -> Either String ([t], s)
... isn't the same as the 'nt' you see in this line, so it constrains
'subsome' to a different type than the one you intended -- and indeed
one which can't be unified with the inferred type. (Unless you use
ScopedTypeVariables.)
As Brent suggested, you should probably pull the "subsome" function out
into a top-level function in any case.
Cheers,
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