Module lexical_analyzer {
	a$={/*
	  All lexical tokens - not syntactically correct, but that will
	  have to wait until syntax analysis
	 */
	/* Print   */  print    /* Sub     */  -
	/* Putc    */  putc     /* Lss     */  <
	/* If      */  if       /* Gtr     */  >
	/* Else    */  else     /* Leq     */  <=
	/* While   */  while    /* Geq     */  >=
	/* Lbrace  */  {        /* Eq      */  ==
	/* Rbrace  */  }        /* Neq     */  !=
	/* Lparen  */  (        /* And     */  &&
	/* Rparen  */  )        /* Or      */  ||
	/* Uminus  */  -        /* Semi    */  ;
	/* Not     */  !        /* Comma   */  ,
	/* Mul     */  *        /* Assign  */  =
	/* Div     */  /        /* Integer */  42
	/* Mod     */  %        /* String  */  "String literal"
	/* Add     */  +        /* Ident   */  variable_name
	/* character literal */  '\n'
	/* character literal */  '\\'
	/* character literal */  ' '
	}
	lim=Len(a$)
	LineNo=1
	ColumnNo=1
	Document Output$
	Buffer Scanner as Integer*lim
	Return Scanner, 0:=a$
	offset=0
	buffer1$=""
	flag_rem=true
	Ahead=lambda Scanner (a$, offset)->{
		=false
		Try {
			\\ second parameter is the offset in buffer units
			\\ third parameter is length in bytes
			=Eval$(Scanner, offset,2*len(a$))=a$
		}
	}
	Ahead2=lambda Scanner (a$, offset)->{
		=false
		Try {
			=Eval$(Scanner, offset,2) ~ a$
		}
	}
	const nl$=chr$(13)+chr$(10), quo$="""", er$="@", Ansi=3
	Try {
		Do
		If Ahead("/*", offset) Then {
			offset+=2 : 	ColumnNo+=2
			While not Ahead("*/", offset)
				If Ahead(nl$, offset) Then
					lineNo++: ColumnNo=1 : offset+=2
				Else
					offset++ : ColumnNo++
				End If
				if offset>lim then
					Error "End-of-file in comment. Closing comment characters not found"+er$
				End if
			End While
			offset+=2 : ColumnNo+=2
		} Else.if Ahead(nl$, offset) Then{
			LineNo++: ColumnNo=1
			offset+=2
		} Else.if Ahead(quo$, offset) Then {
			Output$=format$("{0::-10}{1::-10} ", LineNo, ColumnNo)
			offset++ : ColumnNo++
			strin=offset
			While not Ahead(quo$, offset)
				If Ahead("/", offset) Then
					offset+=2 : ColumnNo+=2
				else
					offset++ : ColumnNo++
				End if
				checkerror()
			End While
			Output$="String "+quote$(Eval$(Scanner, strin, (offset-strin)*2))+nl$
			offset++ : ColumnNo++
		} Else.if Ahead("'", offset) Then {
			Output$=format$("{0::-10}{1::-10} ", LineNo, ColumnNo)
			offset++ : ColumnNo++
			strin=offset
			While not Ahead("'", offset)
				If Ahead("/", offset) Then
					offset+=2 : ColumnNo+=2
				else
					offset++ : ColumnNo++
				End if
				checkerror()
			End While
			lit$=format$(Eval$(Scanner, strin, (offset-strin)*2))
			select case len(lit$)
			case 1
				Output$="Integer "+str$(asc(lit$),0)+nl$
			case >1
				{Error "Multi-character constant."+er$}
			case 0
				{Error "Empty character constant."+er$}
			end select
			offset++ : ColumnNo++
		} Else.if Ahead2("[a-z]", offset) Then {
			strin=offset
			Output$=format$("{0::-10}{1::-10} ", LineNo, ColumnNo)
			offset++ : ColumnNo++
			While Ahead2("[a-zA-Z0-9_]", offset)
					offset++ : ColumnNo++
			End While
			Keywords(Eval$(Scanner, strin, (offset-strin)*2))
		} Else.if Ahead2("[0-9]", offset) Then {
			strin=offset
			Output$=format$("{0::-10}{1::-10} Integer ", LineNo, ColumnNo)
			offset++ : ColumnNo++
			While Ahead2("[0-9]", offset)
					offset++ : ColumnNo++
			End While
			if Ahead2("[a-zA-Z_]", offset) then
				{Error " Invalid number. Starts like a number, but ends in non-numeric characters."+er$}
			else
				Output$=Eval$(Scanner, strin, (offset-strin)*2)+nl$
			end if
		} Else {
			Symbols(Eval$(Scanner, Offset, 2))		
			offset++ : ColumnNo++
		}
		Until offset>=lim
	}
	er1$=leftpart$(error$,er$)
	if er1$<>"" then
		Print
		Report "Error:"+er1$
		Output$="(Error)"+nl$+"Error:"+er1$
	else
		Output$=format$("{0::-10}{1::-10}", LineNo, ColumnNo)+" End_of_Input"+nl$
	end if
	Clipboard Output$
	Save.Doc Output$, "lex.t", Ansi
	document lex$
	Load.Doc lex$,"lex.t", Ansi
	Report lex$
	
	Sub Keywords(a$)
		select case a$
		case "if"
			a$="Keyword_if"
		case "else"
			a$="Keyword_else"
		case "while"
			a$="Keyword_while"
		case "print"
			a$="Keyword_print"
		case "putc"
			a$="Keyword_putc"
		else case
			a$="Identifier "+a$
		end select
		Output$=a$+nl$
	End sub
	Sub Symbols(a$)
		select case a$
		case " ", chr$(9)
			a$=""
		case "("
			a$="LeftParen"
		case ")"
			a$="RightParen"
		case "{"
			a$="LeftBrace"
		case "}"
			a$="RightBrace"
		case ";"
			a$="Semicolon"
		case ","
			a$="Comma"
		case "*"
			a$="Op_multiply"
		case "/"
			a$="Op_divide"
		case "+"
			a$="Op_add"
		case "-"
			a$="Op_subtract"
		case "%"
			a$="Op_mod"
		case "<"
		{	if Ahead("=", offset+1) Then
				offset++
				a$="Op_lessequal"
				ColumnNo++
			else
				a$="Op_less"
			end if
		}
		case ">"
		{	if Ahead("=", offset+1) Then
				offset++
				ColumnNo++
				a$="Op_greaterequal"
			else
				a$="Op_greater"
			end if
		}
		case "="
		{	if Ahead("=", offset+1) Then
				offset++
				ColumnNo++
				a$="Op_equal"
			else
				a$="Op_assign"
			end if
		}
		case "!"
		{	if Ahead("=", offset+1) Then
				offset++
				ColumnNo++
				a$="Op_notequal"
			else
				a$="Op_not"
			end if
		}
		case "&"
		{	if Ahead("&", offset+1) Then
				offset++
				ColumnNo++
				a$="Op_and"
			else
				a$=""
			end if
		}
		case "|"
		{	if Ahead("|", offset+1) Then
				offset++
				ColumnNo++
				a$="Op_or"
			else
				a$=""
			end if
		}
		else case
			{Error "Unrecognized character."+er$}
		end select
		if a$<>"" then
		Output$=format$("{0::-10}{1::-10} ", LineNo, ColumnNo)+a$+nl$
		end if
	End Sub
	Sub checkerror()
		if offset>lim then {
			Error "End-of-line while scanning string literal. Closing string character not found before end-of-line."+er$
		} else.if  Ahead(nl$,offset) then {
			Error "End-of-file while scanning string literal. Closing string character not found."+er$
		}
	End Sub
}
lexical_analyzer