{
module Lexer
open System
open Parser
open Microsoft.FSharp.Text.Lexing
}

// These are some regular expression definitions
let digit = ['0'-'9']
let nondigit = [ 'a'-'z' 'A'-'Z' '_' ]
let idchar = (nondigit | digit)
let whitespace = [' ' '\t' ]
let newline = ('\n' | '\r' '\n')

rule tokenize = parse
| whitespace    { tokenize lexbuf }
| newline       { tokenize lexbuf }
// operators
| "=="          { EQ }
| "!="          { NEQ }
| "+"           { PLUS }
| "-"           { MINUS }
| "*"           { STAR }
| "<"           { LESS }
| "<="          { ATMOST }
| "and"         { AND }
| "or"          { OR }
| "not"         { NOT }
| "old"         { OLD }
| "."           { DOT }
// misc
| "("           { LPAREN }
| ")"           { RPAREN }
| ";"           { SEMI }
| ":="          { ASSIGN }
// keywords
| "procedure"   { PROCEDURE }
| "requires"    { REQUIRES }
| "ensures"     { ENSURES }
| "do"          { DO }
| "end"         { END }
| "new"         { NEW }
| "if"          { IF }
| "then"        { THEN }
| "else"        { ELSE }
| "while"       { WHILE }
| "invariant"   { INVARIANT }
| "call"        { CALL }
| "assert"      { ASSERT }
// literals
| ['-']?digit+  { INT32 (Int32.Parse(LexBuffer<char>.LexemeString lexbuf)) }
| "null"        { NULL }
// identifiers
| idchar+       { ID (LexBuffer<char>.LexemeString lexbuf) }
// EOF
| eof   { EOF }