# GroteTrap

### From HaskellWiki

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m (improved example) |
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'''GroteTrap''' allows you to quickly define expression languages. It is [http://hackage.haskell.org/cgi-bin/hackage-scripts/package/GroteTrap available for download] on Hackage. | '''GroteTrap''' allows you to quickly define expression languages. It is [http://hackage.haskell.org/cgi-bin/hackage-scripts/package/GroteTrap available for download] on Hackage. | ||

− | + | == Example: Logic == | |

<haskell> | <haskell> | ||

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> readExpression logicLanguage "p && q -> r" | > readExpression logicLanguage "p && q -> r" | ||

Impl (And [Var "p",Var "q"]) (Var "r") | Impl (And [Var "p",Var "q"]) (Var "r") | ||

+ | |||

+ | </haskell> | ||

+ | |||

+ | == Example: Arithmetic == | ||

+ | |||

+ | <haskell> | ||

+ | |||

+ | 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 | ||

</haskell> | </haskell> | ||

[[Category:Libraries]] | [[Category:Libraries]] |

## Revision as of 13:11, 28 June 2008

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

## 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 "!" , Nary And True 1 "&&" , Nary Or True 2 "||" , Binary Impl InfixR 3 "->" ] }

With this, we can do:

> readExpression logicLanguage "p && q -> r" Impl (And [Var "p",Var "q"]) (Var "r")

## 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