BASIC

BASIC is the simple implementation that designed to demonstrate such techniques as recursive descent parser and threaded code.

It is designed for .NET Core and uses the expression trees and the dynamic type variables.

It also demonstrates dependency injection and unit testing.

The solution is refactored to contain single project.

Quick Start

Run basic.exe to start BASIC. You'll see the prompt:

basic 1.0.0.0.
_

Type quit end press Enter to exit.

Use sqare brackets with arrays:

_ dim a[10]
A[10] created.
_ for i = 1 to 10 a[i] = i next i
10
_ for i = 1 to 10 print a[i] next i
1
2
3
4
5
6
7
8
9
10

Grammar

start-rule	: INTEGER ('NEXT' | statement)
		| statement
		;

statement	: 'DIM' IDENTIFIER array
		| 'RANDOMIZE' expression
		| 'PRINT' expressions ';'?
		| 'INPUT' (STRING ',')? l-value
		| 'IF' condition 'THEN' statement ('ELSE' statement)?
		| 'FOR' l-value '=' expression 'TO' expression ('STEP' expression)? (statement 'NEXT')?
		| 'GOTO' expression
		| 'REMOVE' range
		| 'LIST' range?
		| 'SAVE' STRING?
		| 'LOAD' STRING
		| 'REM' COMMENT
		| 'RUN'
		| 'END'
		| 'QUIT'
		| 'LET'? assignment
		;

assignment	: l-value '=' expression
		;

range		: INTEGER ('-' INTEGER)?
		;

condition	: or-operands
		;

or-operands	: or-operand ('OR' | 'XOR' or-operands)?
		;

or-operand	: and-operands
		;

and-operands	: and-operand ('AND' and-operands)?
		;

and-operand	: not-operand
		;

not-operand	: 'NOT' not-operand
		| '(' condition ');
		| relation
		;

relation	: expression '=' expression
		| expression '<>' expression
		| expression '<' expression
		| expression '>' expression
		| expression '<=' expression
		| expression '>=' expression
		;

expressions	: expression (',' expressions)?
		;

expression	: add-operands
		;

add-operands	: add-operand ('+' | '-' add-operands)?
		;

add-operand	: mul-operands
		;

mul-operands	: mul-operand ('*' | '/' | 'MOD' mul-operands)?
		;

mul-operand	: un-operand
		;

un-operand	: value ('^' pow-operands)?

pow-operands	: pow-operand ('^' pow-operands)?
		;


pow-operand	: '-' mul-operand
		| '+' mul-operand
		| value
		;

value		: constant
		| l-value
		| function '(' expressions? ')'
		| '(' expression ')'
		;

l-value		: IDENTIFIER array-suffix?
				;

array-suffix	: '[' expressions ']'
		;

constant	: INTEGER
		| FLOAT
		| STRING
		;

function	: 'RND'
		| 'LEN'
		| 'STR'
		| 'CHR'
		| 'ASC'
		| 'MID'
		| 'UPPER'
		| 'LOWER'
		| 'TRIM'
		| 'INSTR'
		| 'INSTRREV'
		| 'REPLACE'
		| 'JOIN'
		| 'SPLIT'
		| 'ABS'
		| 'SIGN'
		| 'MAX'
		| 'MIN'
		| 'EXP'
		| 'LN'
		| 'LOG'
		| 'SQRT'
		| 'SIN'
		| 'COS'
		| 'TAN'
		| 'ASIN'
		| 'ACOS'
		| 'ATAN'
		| 'ATAN2'
		| 'CEIL'
		| 'FLOOR'
		;