Write You a Haskell Stephen Diehl

Alex
Our lexer module will export our Token definition and a function for converting an arbitrary String into
a token stream or a list of Tokens.
{
module Lexer (
Token(..),
scanTokens
) where
import Syntax
}
e tokens are simply an enumeration of the unique possible tokens in our grammar.
data Token
= TokenLet
| TokenTrue
| TokenFalse
| TokenIn
| TokenLambda
| TokenNum Int
| TokenSym String
| TokenArrow
| TokenEq
| TokenAdd
| TokenSub
| TokenMul
| TokenLParen
| TokenRParen
| TokenEOF
deriving (Eq,Show)
scanTokens :: String -> [Token]
scanTokens = alexScanTokens
e token definition is list of function definitions mapping atomic character and alphabetical sequences
to constructors for our Token datatype.
%wrapper ”basic”
$digit = 0-9
$alpha = [a-zA-Z]
$eol = [\n]
130