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|
{
-- only list imports here
import Data.Char
}
%tokentype { Token }
%lexer { lexer } { TokenEOF }
%token
'*' { Sym '*' }
'+' { Sym '+' }
'-' { Sym '-' }
'(' { Sym '(' }
')' { Sym ')' }
i { AnInt $$ }
%%
E :: {Int}
: E '+' E { $1 + $3 }
| E '*' E { $1 * $3 }
| E '-' E { $1 - $3 }
| '(' E ')' { $2 }
| i { $1 }
{
data Token
= TokenEOF
| Sym Char
| AnInt Int
deriving (Show,Eq, Ord)
lexer :: String -> [Token]
lexer [] = []
lexer (' ':cs) = lexer cs
lexer (c:cs) | c `elem` "+*-()"
= Sym c : lexer cs
lexer (c:cs) | isDigit c
= let (yes,no) = span isDigit cs in AnInt (read $ c:yes) : lexer no
}
|
