TypeScript Compiler

This README.md contains high-level detail about the coursework and language from the submitted report.

See individual .mds for detail on the:

• Lexical Analyser
• Parser
• Code Generator
• Code Optimiser

Usage

Install dependencies:

• npm i
• A form of g++ in ENV (e.g. MinGW)

For hello world:

npm start .\test\scripts\hello-world.ts

Or, in general:

npm start <script>

Introduction

The scope of this coursework is to implement a compiler for a source language that has no run-time errors but may issue run-time warnings.

Source Language

The source language for the compiler is chosen to be a subset of TypeScript. TypeScript is an open-source programming language, which is a strict syntactical superset of JavaScript and adds static typing to the language [1], as opposed to JavaScript’s no static type nature [2]. Due to the open-source nature of it, access to its language specification is public. Along with this, since the language is widely used, running [3] and comparing original code during tests [4] will be made easier. The subset chosen is described in the Description of Source Language section.

Target Language

The target language chosen is C. This was mainly chosen due to the low-level nature of the language, allowing for complex algorithms to be executed at close to machine clock. Also, development is made easier due to existing familiarity with the language from previously assessed coursework, most notably CS1PR16 C/C++ labs and CS1FC16 sorting coursework in C.

Implementation Language

The language chosen for the compiler is also TypeScript. This was done to build more familiarity with the programming language, with a view of using it for future projects (most notably, the upcoming final year project). Also, with the rather simple nature of the chosen subset of the language, and the performance of the development machines, some efficiency is traded for greater flexibility of the compiler.

Description of Source Language

Description

For the compiler to be implemented and tested, the source language is defined. Since TypeScript has a very large grammar, a subset of it is chosen and defined.

The main feature required in the subset is output. TypeScript allows standard output to the command-line using its console.log(content) function. As a result, both console and log are added as reserved keywords for the compiler to detect output to stdout. In this case, content can be either a constant or a variable, as seen in Figure 1 and Figure 2 respectively.

    console.log("Hello, world!")

Figure 1. Standard Output with Constant Example

    let num: number = 3
    console.log(num)

Figure 2. Standard Output with Identifier Example

Along with this, the let keyword is added to the reserved list, for use in variable declarations. TypeScript allows multiple types of variables to be declared, and the main ones chosen in the subset are string and number types. Although in Typescript the number types are stored as floating-point values [5], they will be restricted to integers for this application. Along with this, a constant may be added to the declaration to assign a value to the newly declared variable.

Examples of valid declaration statements are shown in Figure 3.

    let num: number
    let str: string

Figure 3. Declare Statements

Examples of valid declare and assign statements are shown in Figure 4.

    let num: number = 3
    let str: string = "Hello, world!"

Figure 4. Declare and Assign Statements

Assignment may be performed outside of the declaration, as seen in Figure 5.

    let str: string
    str = "Hello, world!"

Figure 5. Assign Statements with Constants

Previous assignment statements use constants as the value. Valid assignment statements also allow identifiers to be used, as seen in Figure 6.

    let str: string
    let hello: string = "Hello, world!"
    str = hello

Figure 6. Assign Statements with Identifiers

Arithmetic may be performed in assignment statements as well on number typed variables, as seen in Figure 7.

    let a: number = 1
    let b: number = 2
    let c: number
    c = a + b

Figure 7. Assign Statements with Arithmetic

Along with addition, other available arithmetic operations in the subset are: subtraction, multiplication, incrementation, decrementation.