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.. _syntax-stolen:
Summary of stolen syntax
------------------------
Turning on an option that enables special syntax *might* cause working
Haskell 98 code to fail to compile, perhaps because it uses a variable
name which has become a reserved word. This section lists the syntax
that is "stolen" by language extensions. We use notation and nonterminal
names from the Haskell 98 lexical syntax (see the Haskell 98 Report). We
only list syntax changes here that might affect existing working
programs (i.e. "stolen" syntax). Many of these extensions will also
enable new context-free syntax, but in all cases programs written to use
the new syntax would not be compilable without the option enabled.
There are two classes of special syntax:
- New reserved words and symbols: character sequences which are no
longer available for use as identifiers in the program.
- Other special syntax: sequences of characters that have a different
meaning when this particular option is turned on.
The following syntax is stolen:
``forall``
.. index::
single: forall
Stolen (in types) by default (see :ref:`infelicities-lexical`). ``forall`` is
a reserved keyword and never a type variable, in accordance with `GHC Proposal #43
<https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0043-forall-keyword.rst>`__.
``mdo``
.. index::
single: mdo
Stolen by: :extension:`RecursiveDo`
``foreign``
.. index::
single: foreign
Stolen by: :extension:`ForeignFunctionInterface`
``rec``, ``proc``, ``-<``, ``>-``, ``-<<``, ``>>-``, ``(|``, ``|)``
.. index::
single: proc
Stolen by: :extension:`Arrows`
``?varid``
.. index::
single: implicit parameters
Stolen by: :extension:`ImplicitParams`
``[|``, ``[e|``, ``[p|``, ``[d|``, ``[t|``, ``[||``, ``[e||``
.. index::
single: Quasi-quotes
Stolen by: :extension:`QuasiQuotes`. Moreover, this introduces an ambiguity
with list comprehension syntax. See the
:ref:`discussion on quasi-quoting <quasi-quotes-list-comprehension-ambiguity>`
for details.
``$(``, ``$$(``, ``$varid``, ``$$varid``
.. index::
single: Template Haskell
Stolen by: :extension:`TemplateHaskell`
``[varid|``
.. index::
single: quasi-quotation
Stolen by: :extension:`QuasiQuotes`
⟨varid⟩, ``#``\ ⟨char⟩, ``#``, ⟨string⟩, ``#``, ⟨integer⟩, ``#``, ⟨float⟩, ``#``, ⟨float⟩, ``##``
Stolen by: :extension:`MagicHash`
``(#``, ``#)``
Stolen by: :extension:`UnboxedTuples`
⟨varid⟩, ``!``, ⟨varid⟩
Stolen by: :extension:`BangPatterns`
``pattern``
Stolen by: :extension:`PatternSynonyms`
``static``
Stolen by: :extension:`StaticPointers`
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