rehdi93 / redbasic

RedBasic

A simple basic implementation

This is a implementation of the BASIC programing language in python. It's based on TinyBasic, but not intented to be compatible with it.

Expression precendence (low to high)

• sequence
• assignment
• logical or
• logical and
• equality
• relational
• additive
• multiplicitave
• unary
• lhs expression
• primary

Formal definition

program
    : line_list EOF
    ;

line_list
    : line line_list
    | label line_list
    ;

line
    : integer? statement EOL
    ;

label
    : identifier ':'
    ;

statement 
    : print_stmt
    | input_stmt
    | let_stmt
    | goto_stmt
    | gosub_stmt
    | return_stmt
    | if_stmt
    | comment
    | clear_stmt
    | run_stmt
    | list_stmt
    | end_stmt
    ;

print_stmt
    : 'PRINT' printlist
    | 'PR' printlist
    ;

printlist
    : printitem
    | printitem ':'
    | printitem print_sep printlist
    ;

print_sep 
    : ','
    | ';'
    ;

printitem 
    : single_expression
    | string_literal
    ;

input_stmt
    : 'INPUT' varlist
    ;

let_stmt
    : 'LET' identifier = expression
    | identifier = expression
    ;

goto_stmt
    : 'GOTO' expression
    ;

gosub_stmt
    : 'GOSUB' expression
    ;

return_stmt
    : 'RETURN'
    ;

if_stmt
    : 'IF' expression relop expression 'THEN'? statement
    | 'IF' expression relop expression 'THEN'? statement 'else' statement
    ;

comment
    : 'REM' comment_string
    ;

clear_stmt
    : 'CLEAR'
    ;

run_stmt
    : 'RUN'
    | 'RUN' ',' exprlist
    ;

list_stmt
    : 'LIST'
    | 'LIST' exprlist
    | 'LIST' exprlist list_mode
    ;

list_mode
    : 'code'
    | 'ast'
    ;

end_stmt
    : 'end'
    ;

varlist 
    : identifier
    | identifier ',' varlist
    ;

exprlist 
    : expression
    | expression ',' exprlist
    ;

expression 
    : assignment_expr
    | assignment_expr ',' expression
    ;

assignment_expr
    : logical_or_expr
    | lhs assignment_op assignment_expr
    ;

single_expression
    : assignment_expr
    ;

logical_or_expr
    : logical_and_expr
    | logical_and_expr logical_or_op logical_or_expr
    ;

logical_and_expr
    : equality_expr
    | equality_expr logical_and_op logical_and_expr
    ;

equality_expr
    : relational_expr
    | relational_expr equality_op equality_expr
    ;

relational_expr
    : additive_expr
    | additive_expr relational_op relational_expr
    ;

additive_expr
    : multiplicative_expr
    | multiplicative_expr additive_op additive_expr
    ;

multiplicative_expr
    : unary_expr
    | unary_expr multiplicative_op multiplicative_expr
    ;

unary_expr
    : primary_expr
    | additive_op unary_expr
    | logical_not_op unary_expr
    ;

primary_expr
    : literal
    | paren_expr
    | identifier
    | function
    ;

lhs
    : identifier
    ;

function 
    : 'RND' '(' expression ')'
    | 'USR' '(' exprlist ')'
    ;

number
    : integer
    | float
    ;

identifier
    : [a-zA-Z_]\w*
    ;

integer
    : \d+
    ;

float
    : (\d+\.\d*)([Ee][-+]?\d+)?
    ;

relational_op 
    : '<'
    | '>'
    | '<='
    | '>='
    ;

equality_op
    : '=='
    | '<>'
    | '><'
    ;

assignment_op
    : '='
    | '+='
    | '-='
    | '*='
    | '/='
    ;

additive_op
    : '+'
    | '-'
    ;

multiplicative_op
    : '*'
    | '/'
    ;

logical_or_op
    : '||'
    ;

logical_and_op
    : '&&'
    ;

logical_not_op
    : '!'
    ;