The Lexer

Our initial language has very simple lexical syntax.

integer: 1, -2, 42

integer :: Parser Integer
integer = Tok.integer lexer

float: 3.14, 2.71, 0.0

float :: Parser Double
float = Tok.float lexer

identifier: a, b, foo, ncc1701d

identifier :: Parser String
identifier = Tok.identifier lexer

And several tokens which enclose other token(s) returning a compose expression.

parens :: Parser a -> Parser a
parens = Tok.parens lexer
semiSep :: Parser a -> Parser [a]
semiSep = Tok.semiSep lexer
commaSep :: Parser a -> Parser [a]
commaSep = Tok.commaSep lexer

Lastly our lexer requires that several tokens be reserved and not used as identifiers, we reference these as separately.

reserved: def, extern

reservedOp: +, *, -, ;

reserved :: String -> Parser ()
reserved = Tok.reserved lexer

reservedOp :: String -> Parser ()
reservedOp = Tok.reservedOp lexer

Putting it all together we have our Lexer.hs module.

module Lexer where
import Text.Parsec.String (Parser)
import Text.Parsec.Language (emptyDef)
import qualified Text.Parsec.Token as Tok
lexer :: Tok.TokenParser ()
lexer = Tok.makeTokenParser style
  where
    ops = ["+","*","-",";"]
    names = ["def","extern"]
    style = emptyDef {
               Tok.commentLine = "#"
             , Tok.reservedOpNames = ops
             , Tok.reservedNames = names
             }
integer :: Parser Integer
integer = Tok.integer lexer
float :: Parser Double
float = Tok.float lexer
parens :: Parser a -> Parser a
parens = Tok.parens lexer
commaSep :: Parser a -> Parser [a]
commaSep = Tok.commaSep lexer
semiSep :: Parser a -> Parser [a]
semiSep = Tok.semiSep lexer
identifier :: Parser String
identifier = Tok.identifier lexer
reserved :: String -> Parser ()
reserved = Tok.reserved lexer
reservedOp :: String -> Parser ()
reservedOp = Tok.reservedOp lexer