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module Syntax where<br />
data Expr<br />
= Tr<br />
| Fl<br />
| Zero<br />
| IsZero Expr<br />
| Succ Expr<br />
| Pred Expr<br />
| If Expr Expr Expr<br />
deriving (Eq, Show)<br />
Parser<br />
Much like before our parser is simply written in monadic blocks, each mapping a set of patterns to a<br />
construct in our Expr type. e toplevel entry point to our parser is the expr function which we can<br />
parse with by using the Parsec function parse.<br />
prefixOp s f = Ex.Prefix (reservedOp s >> return f)<br />
-- Infix operators<br />
table :: Ex.OperatorTable String () Identity Expr<br />
table = [<br />
[<br />
prefixOp ”succ” Succ<br />
, prefixOp ”pred” Pred<br />
, prefixOp ”iszero” IsZero<br />
]<br />
]<br />
-- if/then/else<br />
ifthen :: Parser Expr<br />
ifthen = do<br />
reserved ”if”<br />
cond
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