BASIC language syntax

program : line CR (line)*
    
line ::= lineNumber statement
            
statement::= PRINT print-list
             IF expression comparison-operator expression THEN statement
             GOTO lineNumber
             GOSUB lineNumber
             RETURN
             LET var = expression
             INPUT (string ,) var | varString
             BEEP
             CLS (color)
             WAIT number
             COLOR color (,color)
             GET CURSOR var , var
             GET MOUSE var , var , var
             GET GMOUSE var , var , var
             GET MIRROR expression , expression , var
             GET DATA expression , expression , var | varString
             GETCHAR varString , expression , var
             CURSOR expression , expression
             MIRROR expression , expression , expression
             REM
             BOX expression , expression , expression , expression
             PSET expression , expression
             SCROLL expression , expression
             
print-list ::= (string | expression) (, ((string | expression) )*
expression ::= (+ | -) term ( (+ | -) term )*
term ::= factor ((*|/|%) factor)*
factor ::= var | number | operator
lineNumber ::= 1 .. 99999
number ::= digit digit*
digit ::= 0 .. 9
operator ::= tan(expression) | cos(expression) | sin(expression) | RND
comparison-operator ::= < | > | >= | <= | <> | =
var ::= A .. Z
varString ::=  A$ .. Z$
color ::= BLUE | RED | CYAN | GREEN | MAGENTA | YELLOW | WHITE | BLACK | GRAY | PURPLE | ORANGE | BROWN