ok and error tuples in Erlang

{ok, Value} and {error, Reason}: the convention every API keeps.

%% {ok, Value} and {error, Reason}: the convention every API keeps.
lookup("5560199") -> {ok, "Maud's desk"};
lookup("5560142") -> {ok, "front counter"};
lookup(_) -> {error, unlisted}.

main(_) ->
    Numbers = ["5560199", "5550000", "5560142"],
    [case lookup(N) of
         {ok, Where} ->
             io:format("~s rings ~s~n", [N, Where]);
         {error, Reason} ->
             io:format("~s failed: ~p~n", [N, Reason])
     end || N <- Numbers],
    ok.

How it works

Success and failure are just tuples to match on.
case lookup(N) of branches on the tag.
No exceptions needed for expected failures.

Keywords and builtins used here

case
end
format
lookup
main
of

The run, in numbers

Lines: 14
Characters to type: 403
Tokens: 134
Three-star pace: 60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 134 seconds.

Type this snippet

Step 1 of 2 in Errors as data, step 23 of 31 in Language basics.

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