Writing Coq libraries and plugins — Coq 8.12.0 documentation

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# Writing Coq libraries and plugins

This section presents the part of the Coq language that is useful only to library and plugin authors. A tutorial for writing Coq plugins is available in the Coq repository in doc/plugin_tutorial.

## Deprecating library objects or tactics

You may use the following attribute to deprecate a notation or tactic. When renaming a definition or theorem, you can introduce a deprecated compatibility alias using `Notation (abbreviation)` (see the example below).

Attribute `deprecated ( since = string ,? note = string? )`

  At least one of `since` or `note` must be present. If both are present, either one may appear first and they must be separated by a comma.

  This attribute is supported by the following commands: `Ltac`, `Tactic Notation`, `Notation`, `Infix`.

  It can trigger the following warnings:

  Warning `Tactic qualid is deprecated since stringsince. stringnote.`
  Warning `Tactic Notation qualid is deprecated since stringsince. stringnote.`
  Warning `Notation string is deprecated since stringsince. stringnote.`

    `qualid` or `string` is the notation, `stringsince` is the version number, `stringnote` is the note (usually explains the replacement).

Example: Deprecating a tactic.

#[deprecated(since="0.9", note="Use idtac instead.")] Ltac foo := idtac.
  foo is defined
Goal True.
  1 subgoal ============================ True
Proof.
now foo.
  Toplevel input, characters 4-7: > now foo. > ^^^ Warning: Tactic foo is deprecated since 0.9. Use idtac instead. [deprecated-tactic,deprecated] No more subgoals.

Example: Introducing a compatibility alias

Let's say your library initially contained:

Definition foo x := S x.
  foo is defined

and you want to rename `foo` into `bar`, but you want to avoid breaking your users' code without advanced notice. To do so, replace the previous code by the following:

Definition bar x := S x.
  bar is defined
#[deprecated(since="1.2", note="Use bar instead.")] Notation foo := bar (only parsing).

Then, the following code still works, but emits a warning:

Check (foo 0).
  Toplevel input, characters 7-10: > Check (foo 0). > ^^^ Warning: Notation foo is deprecated since 1.2. Use bar instead. [deprecated-syntactic-definition,deprecated] bar 0 : nat

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