diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/bugs.rst | 39 | ||||
| -rw-r--r-- | docs/users_guide/glasgow_exts.rst | 34 | ||||
| -rw-r--r-- | docs/users_guide/using-warnings.rst | 7 |
3 files changed, 60 insertions, 20 deletions
diff --git a/docs/users_guide/bugs.rst b/docs/users_guide/bugs.rst index c0cffa0ee8..4dc49f0328 100644 --- a/docs/users_guide/bugs.rst +++ b/docs/users_guide/bugs.rst @@ -49,6 +49,45 @@ Lexical syntax reserving ``forall`` as a keyword has significance. For instance, GHC will not parse the type signature ``foo :: forall x``. +- The ``(!)`` operator, when written in prefix form (preceded by whitespace + and not followed by whitespace, as in ``f !x = ...``), is interpreted as a + bang pattern, contrary to the Haskell Report, which prescribes to treat ``!`` + as an operator regardless of surrounding whitespace. Note that this does not + imply that GHC always enables :extension:`BangPatterns`. Without the + extension, GHC will issue a parse error on ``f !x``, asking to enable the + extension. + +- Irrefutable patterns must be written in prefix form:: + + f ~a ~b = ... -- accepted by both GHC and the Haskell Report + f ~ a ~ b = ... -- accepted by the Haskell Report but not GHC + + When written in non-prefix form, ``(~)`` is treated by GHC as a regular + infix operator. + + See `GHC Proposal #229 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0229-whitespace-bang-patterns.rst>`__ + for the precise rules. + +- Strictness annotations in data declarations must be written in prefix form:: + + data T = MkT !Int -- accepted by both GHC and the Haskell Report + data T = MkT ! Int -- accepted by the Haskell Report but not GHC + + See `GHC Proposal #229 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0229-whitespace-bang-patterns.rst>`__ + for the precise rules. + +- As-patterns must not be surrounded by whitespace:: + + f p@(x, y, z) = ... -- accepted by both GHC and the Haskell Report + f p @ (x, y, z) = ... -- accepted by the Haskell Report but not GHC + + When surrounded by whitespace, ``(@)`` is treated by GHC as a regular infix + operator. + + See `GHC Proposal #229 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0229-whitespace-bang-patterns.rst>`__ + for the precise rules. + + .. _infelicities-syntax: Context-free syntax diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst index af3d48e0a3..d23681e0b3 100644 --- a/docs/users_guide/glasgow_exts.rst +++ b/docs/users_guide/glasgow_exts.rst @@ -13108,10 +13108,9 @@ enable the quotation subset of Template Haskell (i.e. without splice syntax). The :extension:`TemplateHaskellQuotes` extension is considered safe under :ref:`safe-haskell` while :extension:`TemplateHaskell` is not. -- A splice is written ``$x``, where ``x`` is an identifier, or - ``$(...)``, where the "..." is an arbitrary expression. There must be - no space between the "$" and the identifier or parenthesis. This use - of "$" overrides its meaning as an infix operator, just as "M.x" +- A splice is written ``$x``, where ``x`` is an arbitrary expression. + There must be no space between the "$" and the expression. + This use of "$" overrides its meaning as an infix operator, just as "M.x" overrides the meaning of "." as an infix operator. If you want the infix operator, put spaces around it. @@ -13147,9 +13146,8 @@ The :extension:`TemplateHaskellQuotes` extension is considered safe under See :ref:`pts-where` for using partial type signatures in quotations. -- A *typed* expression splice is written ``$$x``, where ``x`` is an - identifier, or ``$$(...)``, where the "..." is an arbitrary - expression. +- A *typed* expression splice is written ``$$x``, where ``x`` is + is an arbitrary expression. A typed expression splice can occur in place of an expression; the spliced expression must have type ``Q (TExp a)`` @@ -14323,12 +14321,15 @@ Note the following points: f !x = 3 - Is this a definition of the infix function "``(!)``", or of the "``f``" - with a bang pattern? GHC resolves this ambiguity in favour of the - latter. If you want to define ``(!)`` with bang-patterns enabled, you - have to do so using prefix notation: :: + Is this a definition of the infix function "``(!)``", or of the "``f``" with + a bang pattern? GHC resolves this ambiguity by looking at the surrounding + whitespace: :: - (!) f x = 3 + a ! b = ... -- infix operator + a !b = ... -- bang pattern + + See `GHC Proposal #229 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0229-whitespace-bang-patterns.rst>`__ + for the precise rules. .. _strict-data: @@ -14359,6 +14360,13 @@ we interpret it as if they had written :: The extension only affects definitions in this module. +The ``~`` annotation must be written in prefix form:: + + data T = MkT ~Int -- valid + data T = MkT ~ Int -- invalid + +See `GHC Proposal #229 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0229-whitespace-bang-patterns.rst>`__ +for the precise rules. .. _strict: @@ -14393,7 +14401,7 @@ optionally had by adding ``!`` in front of a variable. Adding ``~`` in front of ``x`` gives the regular lazy behavior. - Turning patterns into irrefutable ones requires ``~(~p)`` or ``(~ ~p)`` when ``Strict`` is enabled. + Turning patterns into irrefutable ones requires ``~(~p)`` when ``Strict`` is enabled. diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst index 62b644aa8a..4649f86de0 100644 --- a/docs/users_guide/using-warnings.rst +++ b/docs/users_guide/using-warnings.rst @@ -46,7 +46,6 @@ generally likely to indicate bugs in your program. These are: * :ghc-flag:`-Winaccessible-code` * :ghc-flag:`-Wstar-is-type` * :ghc-flag:`-Wstar-binder` - * :ghc-flag:`-Wspace-after-bang` The following flags are simple ways to select standard "packages" of warnings: @@ -1280,12 +1279,6 @@ of ``-W(no-)*``. per-module basis with :ghc-flag:`-Wno-simplifiable-class-constraints <-Wsimplifiable-class-constraints>`. -.. ghc-flag:: -Wspace-after-bang - :shortdesc: warn for missing space before the second argument - of an infix definition of ``(!)`` when - :extension:`BangPatterns` are not enabled - :type: dynamic - :reverse: -Wno-missing-space-after-bang .. ghc-flag:: -Wtabs :shortdesc: warn if there are tabs in the source file :type: dynamic |