TLang (Test Language)

Simple programming language made in order to learn the basics of creating programming languages.

Features

• declaring variables with optional initial value
• creating binary expressions with operators: +, -, *, /
• creating assignment expressions
• printing values to the console

Example

var x = 3
var y = 2
var z = x * y

print x, y, z

Keywords

var - variable declaration

Syntax:

var IDENTIFIER (PUNCTUATOR(=) BINARY_EXPRESSION)?

---

print - prints values to the console

Syntax:

print EXPRESSION (PUNCTUATOR(,) BINARY_EXPRESSION)*

Implementation

1. Lexical Grammar

1.1. White Space

White space code points are used for tokens separation and to improve source text readability. They may occur between any two tokens and on the start or end of input.

Table 1: White Space Code Points

Code Points	Name	Abbreviation
U+0009	CHARACTER TABULATION	TAB
U+000B	LINE TABULATION	VT
U+000C	FORM FEED	FF
U+FEFF	ZERO WIDTH NO-BREAK SPACE	ZWNBSP
any code point from "Space_Separator" category		USP

1.2. Line Terminators

Line Terminator code points are used for tokens separation and to improve source text readability. As white space code points, they may occur between any two tokens and on the start or end of input.

Table 2: Line Terminator Code Points

Code Points	Name	Abbreviation
U+000A	LINE FEED	LF
U+000D	CARRIAGE RETURN	CR
U+2028	LINE SEPARATOR	LS
U+2029	PARAGRAPH SEPARATOR	PS

Only the Unicode code points in Table 2 are treated as line terminators. Other new line or line breaking Unicode code points are not treated as line terminators but are treated as white space if they meet the requirements listed in Table Table 1. The sequence CR+LF is commonly used as a line terminator. It should be considered as single character for the purpose of reporting line numbers.

1.3. Tokens

Tokens are the smallest indivisible syntactic units of a language

Name	Syntax
KEYWORD	(var|print)
IDENTIFIER	[$_a-zA-Z][$_a-zA-Z0-9]*
NUMBER	[0-9]
PUNCTUATOR	(+|-|*|/|**|,)

2. Expressions

2.1. Binary expression

Binary expression consists of two operands and one operator. The operand can be any number or identifier, but it can also be another binary expression.

Syntax:

(IDENTIFIER|NUMBER|BINARY_EXPRESSION) (PUNCTUATOR(+|-|*|/|**) (IDENTIFIER|NUMBER|BINARY_EXPRESSION))*

2.2. Assignment expression

Assignment expressions are used to assign Binary Expression to the variable.

Syntax:

IDENTIFIER PUNCTUATOR(=) BINARY_EXPRESSION

3. Variable declaration

Variable declarations are initated with var Keyword and they create new variable in memory, which can be accesed by supplied Identifier. It is also possible to assign initial value to the variable, which is Binary Expression.

Syntax:

var IDENTIFIER (PUNCTUATOR(=) BINARY_EXPRESSION)?

4. Printing to the conosole

Printing to the console allows to see results of computations.

Syntax:

print (IDENTIFIER|BINARY_EXPRESSION) (PUNCTUATOR(,) (IDENTIFIER|BINARY_EXPRESSION))*