Perl is very tricky. Its syntax is undecidable, so unless you run the program it's not possible to construct a syntax tree given input (in the general case, it'

Perl is very tricky. Its syntax is undecidable, so unless you run the program it's not possible to construct a syntax tree given input (in the general case, it's possible to make heuristics that will cover 99%) so it requires more brain power compared to easy-to-parse languages like python.