try/catch in Erlang

Three error classes: throw, error, and exit, caught by name.

%% try/catch names the class; throw, error, and exit differ.
risky(bad_number) ->
    throw(unlisted);
risky(cut_line) ->
    error(no_circuit);
risky(Line) ->
    {connected, Line}.

attempt(Input) ->
    try risky(Input) of
        {connected, L} -> io:format("Through on ~p~n", [L])
    catch
        throw:unlisted -> io:format("Not in the book~n");
        error:no_circuit -> io:format("Dead pair, reroute~n")
    end.

main(_) ->
    [attempt(X) || X <- [4, bad_number, cut_line]],
    ok.

How it works

try ... of handles success; catch handles the classes.
throw:unlisted and error:no_circuit match class and reason.
Untouched inputs flow through the of arm normally.

Keywords and builtins used here

attempt
catch
end
format
main
of
risky
try

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Step 2 of 2 in Errors as data, step 24 of 31 in Language basics.

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try/catch in other languages

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