grammar.txt

x=0;
50ms:
clr;
c500,500+sin x,200*sin x;
x++;

program         : variableDec* loop (statement ';')*
variableDec     : ID '=' value ';'
loop            : INT ('ms'|'s') ':'
statement       : clear
                | shape
                | increment
                | decrement
                | variableAssign
                | 

shape           : ('rect' | 'r') value ',' value ',' value ',' value
                | ('circle' | 'c') value ',' value ',' value
                | ('line' | 'l') value ',' value ',' value ',' value
                | ('arc' | 'a') value ',' value ',' value ',' value ',' value ',' value
                
increment       : ID '++'
decrement       : ID '--'

variableAssign  : ID '=' value

value           : value '/' value
                | value '//' value  # Floor division
                | value '*' value  
                | value '+' value
                | value '-' value
                | value '%' value   # Modulo division
                | '%'               # 1000
                | ID                # Variable
                | INT               # Integer

ID              : [a-z]
INT             : [0-9]*