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/
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