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@git.haskell.org wrote:

Repository : ssh://git@git.haskell.org/ghc

On branch : master Link : http://ghc.haskell.org/trac/ghc/changeset/a972bddfc8115d80d774383a55202a293d...

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commit a972bddfc8115d80d774383a55202a293dc68595 Author: Simon Peyton Jones 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.

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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>

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