Folks,
I'm trying to save time when typing in my ASTs so I thought I would
create a Plus class like this (I do hide the one from Prelude)
class PlusClass a b c | a b -> c where
(+) :: a -> b -> c
{-
instance (Integral a, Integral b) => PlusClass a b Expr where
a + b = NumExpr (NumOp Plus (Int (fromIntegral a)) (Int
(fromIntegral b)))
instance Integral a => PlusClass a Double Expr where
a + b = NumExpr (NumOp Plus (Int (fromIntegral a)) (Double b))
-}
instance PlusClass Integer Integer Expr where
a + b = NumExpr (NumOp Plus (Int a) (Int b))
instance PlusClass Double Integer Expr where
a + b = NumExpr (NumOp Plus (Double a) (Int b))
instance PlusClass NumExpr NumExpr Expr where
a + b = NumExpr (NumOp Plus a b)
instance PlusClass Integer NumExpr Expr where
a + b = NumExpr (NumOp Plus (Int a) b)
instance PlusClass NumExpr Integer Expr where
a + b = NumExpr (NumOp Plus a (Int b))
instance PlusClass String String Expr where
a + b = StrExpr (StrOp StrPlus (Str a) (Str b))
NumExpr and StrExpr return Expr whereas Int, Double return NumExpr
and Str returns StrExpr.
This is all so that I could type in
input2 =
[ InputDecs [ inp "emaLength" TyNumber (20 + 40) ] ]
Still, I get the following error
Easy/Test/ParserAST.hs:76:44:
No instance for (PlusClass t t1 Expr)
arising from use of `+' at Easy/Test/ParserAST.hs:76:44-50
Possible fix: add an instance declaration for (PlusClass t t1 Expr)
In the third argument of `inp', namely `(20 + 40)'
In the expression: inp "emaLength" TyNumber (20 + 40)
In the first argument of `InputDecs', namely
`[inp "emaLength" TyNumber (20 + 40)]'
and get an overlapped instances error if I uncomment the top portion.
Any suggestions on how to resolve this?
Thanks, Joel
--
http://wagerlabs.com/
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