For me what's striking about Erlang syntax is the meaning of the semi-colon and the period, as function clause separator. Most of the rest is just vanilla FP lang syntax.
Do you think it is because other programming languages don't uses the semi-colon that way? Or that periods are usually used to access class members, but not to finish function declarations?
The two clauses separated by a semicolon are sentences; thus the semicolon is logically and grammatically equivalent to a full stop. (As long as you normalise the capitalisation). The difference is in nuance, flow, and other soft things.
So when do you use a semicolon instead of a full stop? Whenever you want to!
The really difficult punctuation mark in English is the full colon.