Validity Checker

The purpose of the validity checker is to:

• Reject any return statements outside of function definitions and declarations.
• Reject any return statements inside of while and for loops (that are not in any function definitions and declarations in that loop).
• Reject any assignments to the loop control variable in for loops.
• Reject any assignments to names declared with const or function.
• Annotate any function declaration in a statement sequence as typable, if there are only function declarations before it in the sequence.
• Annotate any const or let declaration in a statement sequence as typable, if its name does not occur in its own right-hand side or in any statement before it in the sequence.

(here goes a more detailed specification: input:..., output:...)