[fenollp]

Yes, the line

    count_characters([H|T], #{ H := N }=X) -> …

is not yet fully understood by the VM. More details on this here [1]. Every other line works fine though. Oh and instead of using maps one can use records, dicts, sets, gb_trees, proplists, …

[1] http://stackoverflow.com/questions/23106543/illegal-pattern-...

[navium]

Agree. But that line is the crux! They should have implemented this match to begin with, to functionally make use of maps!