[erlang-questions] -spec notation for unexported functions?

Kostis Sagonas kostis@REDACTED
Fri Jan 23 09:54:35 CET 2009

Adam Lindberg wrote:
> Hi,
> When using Dialyzer and augmenting the code with -spec specifications, what is the preferred level of brevity? For ALL functions in a module or only for the exported interface functions?   Which way gives a more correct analysis?

This is an excellent question.
My approach is the following:

   - Add specs for *all* exported functions.
     To make sure I have not forgotten any I always compile with the new
     compiler option +warn_missing_spec which warns for missing specs for
     exported functions.  This way, the module interfaces are checked for

   - The above typically is enough, but to see whether some module-local
     function might need a -spec, I run typer in the file (this is very
     simple: typer file.erl) and inspect the specs that typer infers for
     all module local functions.  If they look OK, then I stop there.
     If some of them look too weak, e.g. an argument is inferred to be
     the any() term when I intend to use that argument with an integer(),
     then I add a few -specs for these functions too.  Typically, this
     action strengthens some more inferred -specs for module-local


PS. The emacs support for -specs and -types is indeed missing, but we
     lack the expertise to fix it.  Help on this one is appreciated.

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