users-guide: Add GHCi's ::<builtin-command> form

This commit explicitly adds description about double colon command
of GHCi.

[skip ci]

1 files changed, 9 insertions, 0 deletions

diff --git a/docs/users_guide/ghci.rst b/docs/users_guide/ghci.rst
index 857a03aecd..72e2d66e12 100644
--- a/docs/users_guide/ghci.rst
+++ b/docs/users_guide/ghci.rst
@@ -2994,6 +2994,12 @@ commonly used commands.
 
     The :ghci-cmd:`:uses` command requires :ghci-cmd:`:set +c` to be set.
 
+.. ghci-cmd:: :: ⟨builtin-command⟩
+
+    Executes the GHCi built-in command (e.g. ``::type 3``). That is,
+    look up on the list of builtin commands, excluding defined macros.
+    See also: :ghci-cmd:`:def`.
+
 .. ghci-cmd:: :! ⟨command⟩
 
     .. index::
@@ -3297,6 +3303,9 @@ Here are some examples:
 
    You get ``:type 3`` with your defined macro.
 
+When giving priority to built-in commands, you can use
+:ghci-cmd:`:: ⟨builtin-command⟩`, like ``::type 3``.
+
 .. _dot-haskeline-file:
 
 The ``.haskeline`` file