36 lines
1.5 KiB
ReStructuredText
36 lines
1.5 KiB
ReStructuredText
Ordered Set Language
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====================
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A few fields take an ordered set as argument and can be specified using a small
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DSL.
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Dune interprets this DSL into an ordered set of strings using the
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following rules:
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- ``:standard`` denotes the standard value of the field when it's absent
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- an atom not starting with a ``:`` is a singleton containing only this atom
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- a list of sets is the concatenation of its inner sets
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- ``(<sets1> \ <sets2>)`` is the set composed of elements of ``<sets1>`` that do
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not appear in ``<sets2>``
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In addition, some fields support the inclusion of an external file using the
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syntax ``(:include <filename>)``. For instance, this is useful when you need to
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run a script to figure out some compilation flags. ``<filename>`` is expected to
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contain a single S-expression and cannot contain ``(:include ...)`` forms.
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Note that inside an ordered set, a list's first element cannot be
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an atom except if it starts with ``-`` or ``:``. The reason for this is
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that we're planning to add simple programmatic features in the
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future so that one may write:
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.. code::
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(flags (if (>= %{ocaml_version} 4.08) ...))
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This restriction will allow you to add this feature without introducing
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breaking changes. If you want to write a list where the first element
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doesn't start with ``-``, you can simply quote it: ``("x" y z)``.
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Most fields using the ordered set language also support
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:doc:`../concepts/variables`. Variables are expanded after the set language is
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interpreted.
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