Implement multiple phases of compiler for custom language c--
Data Types: int char
Keywords: def ifelse while ret print read
Arithmetic operators: + - * /
Relational operators: < <= > >= == <>
Line comments: start the line with #
Multi line comments: ## enclose commentin ##
Identifier: a letter followed by any number of letters or digits
Numeric constants: only integers
Literal constants: a letter enclosed in single quotes
Parenthesis, braces, square brackets
Assignment operator: <-
Semi colon: ;
Comma: ,