Xchange

Introduction

Interpreter of simple programming language with currency types. Parsing visualizator can used to debugging and learning basic concepts of interpreters implementation. Exchanges rates are downloaded from the Web.

BNF grammar notation

  program ​= { functionDefinition } . 
  functionDefinition ​= "function" id "(" parameters ")" statementBlock . 
  parameters ​= [ id { "," id } ] . 
  arguments ​= [ assignable [castOp] { "," assignable [castOp] } ] . 
  statementBlock​ = "{" { instructions } "}" . 
  instructions = ifStatement   | returnStatement | whileStatement |  
               initStatement | assignStatement | functionCall   |    
               breakCommand  | continueCommand | statementBlock 


  ifStatement ​= "if" "(" generalCond ")" statementBlock [ "else" statementBlock]. 
  returnStatement ​= "return" assignable ";" . 
  whileStatement​ = "while" "(" generalCond ")" statementBlock . 
  initStatement​ = type id [ assignmentOp assignable ] ";" . 
  assignStatement​ = id assignmentOp assignable ";" . 
  functionCall ​= id "(" arguments ")" ";" .
  breakCommand = "break" ";" .
  continueCommand = "continue" ";" . 

  assignable ​= functionCall [ castOp ] | generalExpr .
  generalExpr ​= multiplicativeExpr {additiveOp multiplicativeExpr} [castOp].
  multiplicativeExpr ​= baseExpr { multiplicativeOp baseExpr } . 
  baseExpr​ = ( number | castableId | nestedExpr ) .
  nestedExpr ​= "(" generalExpr ")" .

  generalCond ​= andCond { orOp andCond } . 
  andCond​ = equalityCond { andOp equalityCond } . 
  equalityCond​ = relationalCond { equalityOp relationalCond } . 
  relationalCond ​= baseCond { relationalOp​ baseCond } . 
  baseCond​ = [ negationOp ] ( nestedCond | castableId | number ) . 
  nestedCond​ = "(" generalCond ")" . 

  negationOp = "!" . 
  assignmentOp ​= "=" . 
  orOp​ = "||" . 
  andOp ​= "&&" . 
  equalityOp​ = "==" | "!=" . 
  relationalOp​ = "<" | ">" | "<=" | ">=" . 
  additiveOp ​= "+" | "-­" .   

Visualization of parsing

Parsing of correct script and incorrect one :

Examples of correct scripts

function factorial(n)
{
	if (n == 1)
	{
		return 1;
	}
	
	return n * factorial(n-1);
}

function pow(num, exp)
{
	var i = 0;
	var result = 1;

	while (1)
	{
		if (i >= exp)
		{
			break;
		}

		result = result * num;

		i = i + 1;
	}

	return result;
}

function sum(a, b)
{
	var i = 0;
	var sum = 0;

	while (i < a)
	{
		sum = sum + b;
		i = i + 1;
	}

	return sum;
}

function main()
{
	printLine(factorial(4));
	printLine(pow(2, 10));
	printLine(sum(5, 100.usd));
	printLine(sum(5, 100).usd);

	return 0;
}