refactor: read_internal_functions_in_yacc

[alexander-akait]

Just refactor for better reading and simplify for better maintenance

In some places we can see unnecessary (extra) checks, but it seems to me that support is more important than speed at the moment

[coveralls]

Coverage increased (+0.01%) to 95.873% when pulling b0d108e on refactor-read_internal_functions_in_yacc into 0df5a49 on master.

[ichiriac]

ok, then just before validating could you try to pass a test with concatenation in order to keep track on the stack size and avoid problems. Lets say $a = 1 + 2 ... until 100 - it can be chaining functions, complex nested closures, etc ... but lets keep it simple, we should garantee to pass 100 concatenation (I've saw worse one time on a real script but I can't remember where)

[alexander-akait]

@ichiriac in acorn 😄 , when you use over +/-/etc 9k you got error, they fixed this, but i think it is not high priority right now, I would like to stabilize the parser at the beginning and then correct such errors, because they are extremely rare in current code, maybe we can merge this as is and i will investigate this in future? We can open issue about this