[commit: ghc] master: Improve documentation of syntax for promoted lists (a972bdd)

[Simon Peyton Jones]

Ah yes, thanks; TypeOperators is needed for the (':), but DataKinds for everything else.

I'll modify.

Simon


|  -----Original Message-----
|  From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of
|  Gabor Greif
|  Sent: 15 December 2014 17:27
|  To: ghc-devs at haskell.org
|  Subject: Re: [commit: ghc] master: Improve documentation of syntax for
|  promoted lists (a972bdd)
|  
|  Hmm, shouldn't that be -XDataKinds (instead of -XTypeOperators)?
|  
|  
|  also:
|    umambiguous ---> unambiguous
|    becuase ---> because
|  
|  Cheers,
|  
|      Gabor
|  
|  On 12/15/14, git at git.haskell.org <git at git.haskell.org> wrote:
|  > Repository : ssh://git@git.haskell.org/ghc
|  >
|  > On branch  : master
|  > Link       :
|  >
|  http://ghc.haskell.org/trac/ghc/changeset/a972bddfc8115d80d774383a5520
|  > 2a293dc68595/ghc
|  >
|  >>---------------------------------------------------------------
|  >
|  > commit a972bddfc8115d80d774383a55202a293dc68595
|  > Author: Simon Peyton Jones <simonpj at microsoft.com>
|  > Date:   Mon Dec 15 17:08:29 2014 +0000
|  >
|  >     Improve documentation of syntax for promoted lists
|  >
|  >     THe documentation in 7.9.4 of promoted list and tuple types was
|  >     misleading, which led to Trac #9882.  This patch makes explicit
|  >     that only type-level with two or more elements can have the
|  >     quote omitted.
|  >
|  >
|  >>---------------------------------------------------------------
|  >
|  > a972bddfc8115d80d774383a55202a293dc68595
|  >  compiler/parser/Parser.y          |  8 ++++++--
|  >  docs/users_guide/glasgow_exts.xml | 19 ++++++++++++++++---
|  >  2 files changed, 22 insertions(+), 5 deletions(-)
|  >
|  > diff --git a/compiler/parser/Parser.y b/compiler/parser/Parser.y
|  index
|  > bffe6e1..235d34a 100644
|  > --- a/compiler/parser/Parser.y
|  > +++ b/compiler/parser/Parser.y
|  > @@ -1483,6 +1483,10 @@ atype :: { LHsType RdrName }
|  >                                                         [mo $2,mc
|  $4] }
|  >          | SIMPLEQUOTE var                       { sLL $1 $> $
|  HsTyVar $
|  > unLoc $2 }
|  >
|  > +        -- Two or more [ty, ty, ty] must be a promoted list type,
|  just as
|  > +        -- if you had written '[ty, ty, ty]
|  > +        -- (One means a list type, zero means the list type
|  constructor,
|  > +        -- so you have to quote those.)
|  >          | '[' ctype ',' comma_types1 ']'  {% ams (sLL $1 $> $
|  > HsExplicitListTy
|  >
|  placeHolderKind ($2 :
|  > $4))
|  >                                                   [mo $1, mj
|  AnnComma
|  > $3,mc $5] } @@ -1503,11 +1507,11 @@ inst_types1 :: { [LHsType
|  RdrName]
|  > }
|  >          | inst_type ',' inst_types1    {% addAnnotation (gl $1)
|  AnnComma
|  > (gl $2)
|  >                                            >> return ($1 : $3) }
|  >
|  > -comma_types0  :: { [LHsType RdrName] }
|  > +comma_types0  :: { [LHsType RdrName] }  -- Zero or more:  ty,ty,ty
|  >          : comma_types1                  { $1 }
|  >          | {- empty -}                   { [] }
|  >
|  > -comma_types1    :: { [LHsType RdrName] }
|  > +comma_types1    :: { [LHsType RdrName] }  -- One or more:  ty,ty,ty
|  >          : ctype                        { [$1] }
|  >          | ctype  ',' comma_types1      {% addAnnotation (gl $1)
|  AnnComma
|  > (gl $2)
|  >                                            >> return ($1 : $3) }
|  diff
|  > --git a/docs/users_guide/glasgow_exts.xml
|  > b/docs/users_guide/glasgow_exts.xml
|  > index e12703f..7edca07 100644
|  > --- a/docs/users_guide/glasgow_exts.xml
|  > +++ b/docs/users_guide/glasgow_exts.xml
|  > @@ -6882,9 +6882,9 @@ is a single quote.</para>  </sect2>
|  >
|  >  <sect2 id="promoted-lists-and-tuples"> -<title>Promoted lists and
|  > tuples types</title>
|  > +<title>Promoted list and tuple types</title>
|  >  <para>
|  > -Haskell's list and tuple types are natively promoted to kinds, and
|  > enjoy the
|  > +With <option>-XTypeOperators</option>, Haskell's list and tuple
|  types
|  > +are
|  > natively promoted to kinds, and enjoy the  same convenient syntax at
|  > the type level, albeit prefixed with a quote:
|  >  <programlisting>
|  >  data HList :: [*] -> * where
|  > @@ -6893,8 +6893,21 @@ data HList :: [*] -> * where
|  >
|  >  data Tuple :: (*,*) -> * where
|  >    Tuple :: a -> b -> Tuple '(a,b)
|  > +
|  > +foo0 :: HList '[]
|  > +foo0 = HNil
|  > +
|  > +foo1 :: HList '[Int]
|  > +foo1 = HCons (3::Int) HNil
|  > +
|  > +foo2 :: HList [Int, Bool]
|  > +foo2 = ...
|  >  </programlisting>
|  > -Note that this requires <option>-XTypeOperators</option>.
|  > +For type-level lists of <emphasis>two or more elements</emphasis>,
|  > +such as the signature of <literal>foo2</literal> above, the quote
|  may
|  > +be
|  > omitted because the meaning is
|  > +umambiguous. But for lists of one or zero elements (as in
|  > <literal>foo0</literal>
|  > +and <literal>foo1</literal>), the quote is required, becuase the
|  > +types
|  > <literal>[]</literal>
|  > +and <literal>[Int]</literal> have existing meanings in Haskell.
|  >  </para>
|  >  </sect2>
|  >
|  >
|  > _______________________________________________
|  > ghc-commits mailing list
|  > ghc-commits at haskell.org
|  > http://www.haskell.org/mailman/listinfo/ghc-commits
|  >
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