Pepe, On Apr 7, 2007, at 2:01 PM, Pepe Iborra wrote:
And without the Integral assumption, you cannot define your instance. So what I would do is to create a thin wrapper:
i = id :: Integer -> Integer
and write:
input2 = [ InputDecs [ inp "emaLength" TyNumber ((i 20) + (i 40)) ] ]
That's what I did but I'm driving to make it even simpler. I would like to add various permutations of Integer, Double and NumExpr, as well as String and StrExpr. This includes Integer/ Integer, Integer/Double, Double/NumExpr, etc. This is standalone code, also at http://hpaste.org/1291#a12 {-# OPTIONS -fglasgow-exts -fallow-overlapping-instances #-} import Prelude hiding ( id, (+), (-), (/), (*), (>), GT, EQ, LT ) newtype VarIdent = VarIdent String instance Show VarIdent instance Eq VarIdent data NumExpr = Int Integer | Double Double | NumOp NumOp NumExpr NumExpr data StrExpr = Str String | StrOp StrOp StrExpr StrExpr data Expr = NumExpr NumExpr | StrExpr StrExpr data Type = TyNumber | TyString data NumOp = Plus | Minus -- ... data StrOp = StrPlus data Statement = Skip | InputDecs [InputDecl] data InputDecl = InputDecl VarIdent Type Expr class PlusClass a b c | a b -> c where (+) :: a -> b -> c -- instance PlusClass a b c => PlusClass b a 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) -- and the functions id = VarIdent inp x ty e = InputDecl (id x) ty e input2 = [ InputDecs [ inp "emaLength" TyNumber (20 + 40) ] ] -- http://wagerlabs.com/