The predicate language allows the user to define simple predicates (Boolean-valued functions) that Dune can evaluate. Here is a semiformal specification of the predicate language:
.. productionlist::
pred : (and `pred` `pred`)
: (or `pred` `pred`)
: (not `pred`)
: :standard
: `element`
The exact meaning of :standard and the nature of :token:`element` depend
on the context. For example, in the case of the :ref:`dune-subdirs`, an
:token:`element` corresponds to file glob patterns. Another example is the user
action :doc:`(with-accepted-exit-codes ...) <actions>`, where an
:token:`element` corresponds to a literal integer.