gistfile1.txt

-- arithmetic operators:
data AExpr = Var String Info
           | IntConst Integer Info
           | Neg AExpr Info
           | ABinary ABinOp AExpr AExpr Info
             deriving (Show, Eq)


aExpression :: Parser AExpr
aExpression = buildExpressionParser aOperators aTerm

bExpression :: Parser BExpr
bExpression = buildExpressionParser bOperators bTerm

aOperators = [ [prefix "-" Neg]
             , [binary "*" (ABinary Multiply) AssocLeft]
             , [binary "/" (ABinary Divide) AssocLeft]
             , [binary "+" (ABinary Add) AssocLeft]
             , [binary "-" (ABinary Subtract) AssocLeft]
             ]

bOperators = [ [prefix "not" (Not)]
             , [binary "and" (BBinary And) AssocLeft]
             , [binary "or"  (BBinary Or) AssocLeft]
             ]

binary  name fun assoc = Infix (do{ reservedOp name; pos <- getPosition; return fun (getInfo pos)}) assoc
prefix  name fun       = Prefix (do{ reservedOp name; pos <- getPosition; return fun (getInfo pos)})
postfix name fun       = Postfix (do{ reservedOp name; pos <- getPosition; return fun (getInfo pos)})