GroteTrap
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GroteTrap allows you to quickly define expression languages. It is available for download on Hackage.
Example: Logic
data Logic
= Var String
| Or [Logic]
| And [Logic]
| Impl Logic Logic
| Not Logic
deriving (Show, Eq)
logicLanguage :: Language Logic
logicLanguage = language
{ variable = Var
, operators =
[ Unary Not Prefix 0 "!"
, Assoc And 1 "&&"
, Assoc Or 2 "||"
, Binary Impl InfixR 3 "->"
]
}
With this, we can do:
> readExpression logicLanguage "p && q -> r"
Impl (And [Var "p",Var "q"]) (Var "r")
Example: Arithmetic
arith :: Language Int
arith = language
{ number = id
, operators =
[ Assoc sum 2 "+"
, Binary (-) InfixL 2 "-"
, Assoc product 1 "*"
, Binary div InfixL 1 "/"
, Binary (^) InfixL 0 "^"
]
, functions = [ function1 abs "abs" ]
}
evalArith :: String -> Int
evalArith = readExpression arith
> evalArith "abs(2 - 3) + abs(4 - 5)"
2