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GroteTrap

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(added arithmetic example)
(updated logicLanguage to reflect the new API)
 
Line 17: Line 17:
 
{ variable = Var
 
{ variable = Var
 
, operators =
 
, operators =
[ Unary Not Prefix 0 "!"
+
[ Unary Not Prefix 0 "!"
, Nary And True 1 "&&"
+
, Assoc And 1 "&&"
, Nary Or True 2 "||"
+
, Assoc Or 2 "||"
, Binary Impl InfixR 3 "->"
+
, Binary Impl InfixR 3 "->"
 
]
 
]
 
}
 
}

Latest revision as of 13:13, 28 June 2008

GroteTrap allows you to quickly define expression languages. It is available for download on Hackage.

[edit] 1 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")

[edit] 2 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