(* mlexer.mll for Scheme *)
(* Stephanie Weirich, Adapted from code by Amr Sabry *)

{
(* Header *)
open EoplParser
open Format

exception Eof
exception LexErr

let lineno   = ref 1
and start    = ref 0

let newline lexbuf = incr lineno; start := (Lexing.lexeme_start lexbuf)

let print_error (str:string) : unit = 
  (print_string "Error at ";
	print_int (!lineno);
	print_string ".";
	print_int (!start);
	print_string ":";
	print_string str)
}

let digit = ['0'-'9']
let letter = ['a'-'z' 'A'-'Z']
let id = '_' | (letter (letter | digit | ['-' '_' '!' '?'])*)
let number = ['1'-'9'] (digit*) | ['0']

rule token = parse
    [' ' '\009' '\012']+  { token lexbuf }   (* skip blanks *)
  | [' ' '\009' '\012']*("\r")?"\n"  (* Count the number of newlines *)    
      { newline lexbuf; token lexbuf }
  |  ';'[^'\n']*'\n'    (* skip comments *)
		{ newline lexbuf; token lexbuf }   
		                      
  |  "proc"           { LAMBDA }
  |  '('              { LPAREN }
  |  ')'              { RPAREN }
  |  "let"            { LET   }
  |  '+'              { PLUS }
  |  '*'              { TIMES }
  |  '-'              { MINUS }  
  |  '='              { EQUAL }
  |  "and"            { AND }
  |  "or"             { OR  }
  |  "not"            { NOT }
  |  "if"             { IF  }
  |  "true"           { TRUE }
  |  "false"          { FALSE }
  |  "in"             { IN }
  |  "then"           { THEN }
  |  "else"           { ELSE } 
  |  ","              { COMMA }
  |  "letrec"         { LETREC }
  |  "set"            { SET } 
  |  "add1"           { ADD1 }
  |  "sub1"           { SUB1 }
  |  "zero?"          { ZERO }
  |  "<"              { LT   }
  |  ">"              { GT   }
  |  id               { ID(Lexing.lexeme lexbuf) }
  |  number           { NUMBER(int_of_string (Lexing.lexeme lexbuf)) }
  |  eof              { raise Eof }

  | _  
      {   failwith ("Illegal character '" ^ (Lexing.lexeme lexbuf) ^ "'")  }


{
(* Trailer *)
}