X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fglasgow_exts.xml;h=a08ace929f371526fc1deb49d94a2bbd0e385c06;hb=f1779d1350e7f30c446e51f3d33355858533fe13;hp=21aba83d33bc25584ee99c8d4e7c15dabe4d9f30;hpb=523101db16170b11b07e9ace7bcdf82eaaaf8c2e;p=ghc-hetmet.git diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml index 21aba83..a08ace9 100644 --- a/docs/users_guide/glasgow_exts.xml +++ b/docs/users_guide/glasgow_exts.xml @@ -335,6 +335,75 @@ Indeed, the bindings can even be recursive. Syntactic extensions + + Unicode syntax + The language + extension + enables Unicode characters to be used to stand for certain ASCII + character sequences. The following alternatives are provided: + + + + + + ASCII + Unicode alternative + Code point + Name + + + + + :: + :: + 0x2237 + PROPORTION + + + + + => + ⇒ + 0x21D2 + RIGHTWARDS DOUBLE ARROW + + + + + forall + ∀ + 0x2200 + FOR ALL + + + + + -> + → + 0x2192 + RIGHTWARDS ARROW + + + + + <- + ← + 0x2190 + LEFTWARDS ARROW + + + + + .. + … + 0x22EF + MIDLINE HORIZONTAL ELLIPSIS + + + + + + The magic hash The language extension allows "#" as a @@ -939,6 +1008,7 @@ This name is not supported by GHC. paper Comprehensive comprehensions: comprehensions with "order by" and "group by", except that the syntax we use differs slightly from the paper. +The extension is enabled with the flag . Here is an example: employees = [ ("Simon", "MS", 80) @@ -2284,6 +2354,16 @@ otherwise is a generalised data type ( +As with other type signatures, you can give a single signature for several data constructors. +In this example we give a single signature for T1 and T2: + + data T a where + T1,T2 :: a -> T a + T3 :: T a + + + + The type signature of each constructor is independent, and is implicitly universally quantified as usual. Different constructors may have different universally-quantified type variables @@ -2613,7 +2693,7 @@ GHC always treats the last parameter of the instance -Deriving clause for classes <literal>Typeable</literal> and <literal>Data</literal> +Deriving clause for extra classes (<literal>Typeable</literal>, <literal>Data</literal>, etc) Haskell 98 allows the programmer to add "deriving( Eq, Ord )" to a data type @@ -2623,11 +2703,11 @@ classes Eq, Ord, Enum, Ix, Bounded, Read, and Show. -GHC extends this list with two more classes that may be automatically derived -(provided the flag is specified): -Typeable, and Data. These classes are defined in the library -modules Data.Typeable and Data.Generics respectively, and the -appropriate class must be in scope before it can be mentioned in the deriving clause. +GHC extends this list with several more classes that may be automatically derived: + + With , you can derive instances of the classes +Typeable, and Data, defined in the library +modules Data.Typeable and Data.Generics respectively. An instance of Typeable can only be derived if the data type has seven or fewer type parameters, all of kind *. @@ -2643,6 +2723,26 @@ In other cases, there is nothing to stop the programmer writing a Typab class, whose kind suits that of the data type constructor, and then writing the data type instance by hand. + + + With , you can derive instances of +the class Functor, +defined in GHC.Base. + + + With , you can derive instances of +the class Foldable, +defined in Data.Foldable. + + + With , you can derive instances of +the class Traversable, +defined in Data.Traversable. + + +In each case the appropriate class must be in scope before it +can be mentioned in the deriving clause. + @@ -5764,6 +5864,8 @@ Wiki page. an expression; the spliced expression must have type Q Exp + an type; the spliced expression must + have type Q Typ a list of top-level declarations; the spliced expression must have type Q [Dec] @@ -5812,7 +5914,7 @@ Wiki page. (Compared to the original paper, there are many differences of detail. The syntax for a declaration splice uses "$" not "splice". The type of the enclosed expression must be Q [Dec], not [Q Dec]. -Type splices are not implemented, and neither are pattern splices or quotations. +Pattern splices and quotations are not implemented.)