tacinterpreter

Three Address Code Interpreter

The ThreeAddressCode Interpreter is a tool for running 3AC instructions in the browser. It is a true interpreter for Three Address Code Instructions. Instead of compiling from source language to machine language, it interprets directly in JavaScript.

Get Started

Setting up the Environment

Copy the ThreeAddressCode.min.js inside your working directory and insert the script tag inside your HTML document.

npm install --save tacinterpreter

Building your First Program

The following code segment will produce an alert with result 7.

const ThreeAddressCode = require('tacinterpreter');

let interpreter = new ThreeAddressCode();
interpreter.run("print 3+4", [], function(out) {
    alert(out);
});

Documentation

Class ThreeAddressCode

Takes Config object to configure the intepreter.

Syntax

var interpreter = new ThreeAddressCode([config]);

Methods

.run()

Method to execute the code segment with the given inputs.

• Parameters

  code (string)

  Code lines separated by the separater defined in the config object

  inputs (array)

  List of inputs referenced in the code segment from p0 to pn.

  print (method)

  Pipe stdout each time a print statement is hit, return Print Object.

  error (method)

  Handles error handling, return Error Object.

• Syntax

   interpreter.run(code, [inputs, [prints, [error]]]);

• Example

   interpreter.run("print 3+4\nprint 2*3");

.run_line()

Method to execute a single code line with the given inputs.

• Parameters

  code (string)

  Code lines separated by the separater defined in the config object

  inputs (array)

  List of inputs referenced in the code segment from p0 to pn.

  print (method)

  Pipe stdout each time a print statement is hit, return Print Object.

  error (method)

  Handles error handling, return Error Object.

  clearHeap (boolean)

  Clears the heap memory to start from the beginning.

• Syntax

   interpreter.run_line(code, [inputs, [print, [error, [clearHeap]]]);

• Example

   interpreter.run_line("print 3+4");

.add()

Method to add a single code line to the list of code lines.

• Parameters

  code (string)

  single code line.

• Syntax

   interpreter.add(code);

• Example

   interpreter.add("print 3+9");

.get()

Method to retrieve variables from the heap or to evaluate expression. Returns the value of the varibale stored in heap or the result of an expression.

• Parameters

  code (string)

  single code line or a variable name

• Syntax

   interpreter.get(code);

• Example

   interpreter.get("A");

.output()

Method to retrieve results of print statements. Returns list of print objects.

• Syntax

   interpreter.output();

.debug() [Development purposes only]

Method to retrieve Heap object from the memory. Debug property must be set in config object

• Syntax

   interpreter.debug();

Objects

Config Object

debug

Shows additional information about errors, warnings, prints and program execution. Default value is false.

stopOnError

Stop execution if error occured in the code. Default value is false.

separater

Used to separate code lines inside code string. Default value is '\n'.

Print Object

val

Contains the result of the expression with the print statement.

line

Contains the line number of the print statement.

Error Object

message

Contains the Error message for readibility.

line

Contains the line number of the instruction that produced the error.

code

Contains an interger value unique to each error type.

• 100 - Undefined Variable
• 101 - Missing Operand
• 102 - Unknown operator
• 104 - Invalid Pointer Reference
• 105 - Invalid Type Conversion
• 106 - Undefined Label
• 107 - Invalid Method call
• 108 - Array index out of bound
• 120 - Unknown Error Type

Executable Commands

Expression

Unary and Binary Operations with optional assignment. Variables can be pointers, references and indexed assignments.

Binary Expression

[variable = ] expression operator expression

Unary Expression

[variable = ] operator expression

Indexed Expression

array[index] = expression

Pointer Expression

variable2 = &variable1
*variable2 = expression
[variable3 =] *variable2

Example

// Stores 7 in a
a = 3 + 4

// Stores 21 in b
b = a * 3

// Stores -21 in c
c = -b

// prints 63
9 * 7

// Create an array with only one index '0' with value '10'
arr[0] = 10

// makes 'h' a pointer pointing to the address of 'a'
h = &a

// modifies the value pointed to by 'h'
*h = 25

Label

Identifier that identifies a labeled statement.

label: [statement]

Example

here: a = 6+7

Jump

Unconditional jumps to a predefined label.

goto label

Example

here: print 8*7
...
goto here

Flow Control

Determine the flow of control based on condition.

if expression statement

Example

if 5 > 3 print 1

Methods

A method can be defined with the keyword BeginFunc and ended with EndFunc.

BeginFunc methodname, n

Create a new method with the name 'methodname' and with number of acceptable parameters 'n'.

EndFunc

Set the boundary for the method code segment. Everything between BeginFunc statement and EndFUnc statement is considered a part of the method body.

param expression

Set a parameter to be passed to the method. Must be called before calling the method. Parameters can be accessed inside the method body with variable names from p0 to pn where n is the number of total parameters.

call methodname, n

Calls a method with the name 'methodname' and acceptable parameters 'n'. The result returned by the method will be stored in the variable 'out' and will be retained until the next method call. Methods must be declared before calling. If there are more paramertes than required for calling the method, the paramertes added first will be send over to the method and removed.

return [expression]

Halts the method execution and returns the value of the expression (if given).

Syntax

BeginFunc methodname, n
statements
EndFunc

param p0
param p1
...
param pn
call methodname, n
print out

Example

This code segment defines a method that returns the multiplication of two numbers.

BeginFunc sum, 2
return p0 * p1
EndFunc

param 6
param 7*5
call sum, 2
print out