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W0018 - Unexpected semicolon or dot

Warning​

-module(main).
foo(1)->2;
foo(2)->3.
      %% ^ warning: Unexpected '.'
foo(3)->4.
-module(main).
foo(1)->2;
foo(2)->3;
      %% ^ warning: Unexpected ';'

Explanation​

The warning message indicates that there is an unexpected separator in a function clause sequence. This diagnostic is generated when:

  1. Unexpected dot (.) - A dot appears where a semicolon is expected between function clauses
  2. Unexpected semicolon (;) - A semicolon appears where a dot is expected at the end of a function definition

In Erlang, function clauses within the same function must be separated by semicolons (;), and the final clause of a function must end with a dot (.).

Correct Pattern:​

function_name(Pattern1) -> Expression1;
function_name(Pattern2) -> Expression2;
function_name(Pattern3) -> Expression3.

To fix this error, replace the incorrect separator with the appropriate one:

  • Use semicolons (;) between function clauses of the same function
  • Use a dot (.) only after the final clause of a function