!
! Implementation of a simple calculator in Triangle by
! - Alexander Constantin constant@rbg.informatik.tu-darmstadt.de
! - Nico Rottstädt rottstae@rbg.informatik.tu-darmstadt.de
!
! This is an excercise from A. Koch's Lecture "Optimierende Compiler",
! summer term 2006 at TU Darmstadt / Germany, course homepage (German):
! http://www.esa.informatik.tu-darmstadt.de/twiki/bin/view/Lectures/OptimierendeCompilerDe.html
!

let

	! --------------
	! String support
	! --------------

	type String ~ record 
		Str: array 80 of Char
	end;

	! Fill a string
	proc readstring(var strg: String) ~
		let
			var chint: Char;
			var length: Integer;
			var testeol : Boolean;
			var testeof : Boolean
		in begin
				length := 0;
				eol(var testeol);
				eof(var testeof);
				while \ testeol /\ \ testeof do begin
					get(var chint);
					strg.Str[length] := chint;
					length := length + 1;
					eol(var testeol);
					eof(var testeof);
				end;
				
				strg.Str[length-2] := '\';
		end;

	! Print a string
	proc putstring(var strg: String) ~
		let
			var i: Integer
		in begin
				i := 0;
				while \ (strg.Str[i] = '\') do begin
					put(strg.Str[i]);
					i := i + 1;
				end;
		end;
		
	! Eliminate spaces in a string
	proc removeSpacesFromString(var strg: String) ~
		let
			var counter : Integer;
			var tmpArray : array 80 of Char;
			var tmpCounter : Integer
		in begin
			counter := 0;
			tmpCounter := 0;
			
			while (strg.Str[counter] \= '\') do begin
				if (strg.Str[counter] \= ' ') then
					begin
						tmpArray[tmpCounter] := strg.Str[counter];
						tmpCounter := tmpCounter + 1;
					end
				else;
				counter := counter + 1;
			end;
			tmpArray[tmpCounter] := strg.Str[counter]; ! copy \      
			strg.Str := tmpArray
		end;
		
	! ---------------
	! Integer support
	! ---------------

	func isDigit(c:Char) : Boolean ~
		(c = '0') \/ (c = '1') \/ (c = '2') \/ (c = '3') \/ (c = '4') \/ 
		(c = '5') \/ (c = '6') \/ (c = '7') \/ (c = '8') \/ (c = '9');
		
	! ord('0') = 48
	! ...
	! ord('9') = 57
	func convertCharToInt(c:Char) : Integer ~
		ord(c) - 48;

	! maxInt = 32767
	! bei char arrays die einen geoesseren Wert darstellen kommt es zum overflow
	proc readInteger(term: array 80 of Char, var i: Integer, var result: Integer) ~
		let
			var isNegative : Boolean
		in begin
			result := 0;

			isNegative := false;
			if (term[i] = '-') then
				begin
					isNegative := true;
					i := i + 1;
				end
			else;
			
			while (isDigit(term[i])) do begin
				result := result * 10;
				result := result + convertCharToInt(term[i]);
				i := i + 1;
			end;

			if (isNegative) then
				result := 0 - result
			else
				
		end;

	! ----------------
	! Calculator stuff
	! ----------------

	! allowed two digit operations: +, -, *, /
	func doOperation(op1 : Integer, op2 : Integer, operator : Char) : Integer ~
		if operator = '+' then
			op1 + op2
		else if operator = '-' then
			op1 - op2
		else if operator = '*' then
			op1 * op2
		else if operator = '/' then
			op1 / op2
		else
			0;

	! rekursives Parsen
	proc parse(term: array 80 of Char, var i: Integer, var result: Integer) ~
		let
			var operand1: Integer;
			var operand2: Integer;
			var operator: Char
		in begin
			if (term[i] = '(') then
				begin

					i := i + 1;
					parse(term, var i, var operand1);
										
					operator := term[i];
					
					i := i + 1;
					parse(term, var i, var operand2);
					
					if (term[i] \= ')') then
						begin
							put('E');
							put('R');
							put('R');
							put('O');
							put('R');
							puteol()
						end
					else
						! do operation here
						i := i + 1;
						result := doOperation(operand1, operand2, operator);
				end
			else
				begin
					readInteger(term, var i, var result)
				end;
		end;


	! Main Program - "Calculator"
	! ---------------------------

	var term : String;
	var result : Integer;
	var i : Integer
	
in begin
		i := 0;
		
		! Prompt ausgeben
		put('T');	
		put('e');	
		put('r');	
		put('m');	
		put(':');	
		put(' ');
		
		! Einlesen des Terms
		readstring(var term);
		removeSpacesFromString(var term);

		! start parsing
		parse(term.Str, var i, var result);
		
		! output result
		puteol();
		putstring(var term);
		put(' ');
		put('=');		
		put(' ');
		putint(result);

		puteol()
end