In the back of my mind, I have for a little while known two things:

• Prolog is no language for a man to use.
• I should probably check out this Erlang thing.

So today I have a look at this getting-started-with-erlang tutorial, and lo! Perhaps my Prolog skills are not so useless after all.

Erlang:

-module(tut4).
-export([list_length/1]).

% simple function to return list length
list_length([]) ->
    0;
list_length([_F|R]) ->
    1 + list_length(R).

Prolog:

% Prolog
:- module(tut4).
:- export list_length/2.

% simple predicate to return list length
list_length([], 0).
list_length([_F|R], L):-
    L is 1 + list_length(R).

Similarities so far:

• Modules - one per file.
• Module/export directives very similar.
• Commas go between statements, full stops end code blocks.
• Comments use the same symbol.
• Multiple function clauses with argument matching.

• Lists work in same manner: [head

  tail].

• Variables begin with capitals.
• Atoms begin with lowercase, (atoms are the same as Ruby’s symbols).
• Singleton variables generate compiler warnings, unless they are prefixed with an underscore (_F above)
• Both scope modules with a colon.
• To quit the shell you call ‘halt’.

Differences:

• Erlang functions have return values, rather than the Prolog concept of success and failure, and passing return values out through arguments.