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diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 1484815..cb5033a 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -131,6 +131,16 @@ documentation describes all the libraries that come with GHC.
+ :
+
+
+ Allow "#" as a postfix modifier on identifiers.
+
+
+
+
+
+
,:
@@ -154,6 +164,38 @@ documentation describes all the libraries that come with GHC.
+
+
+
+
+
+
+
+
+
+
+
+
+ These flags control higher-rank polymorphism.
+ See .
+ New reserved words: forall.
+
+
+
+
+
+
+
+
+
+ Allow more liberal type synonyms.
+ See .
+ New reserved words: forall.
+
+
+
+
+
@@ -170,8 +212,7 @@ documentation describes all the libraries that come with GHC.
- See . Only relevant
- if you also use .
+ See .
@@ -308,7 +349,8 @@ documentation describes all the libraries that come with GHC.
Unboxed types and primitive operations
-GHC is built on a raft of primitive data types and operations.
+GHC is built on a raft of primitive data types and operations;
+"primitive" in the sense that they cannot be defined in Haskell itself.
While you really can use this stuff to write fast code,
we generally find it a lot less painful, and more satisfying in the
long run, to use higher-level language features and libraries. With
@@ -316,28 +358,21 @@ While you really can use this stuff to write fast code,
unboxed version in any case. And if it isn't, we'd like to know
about it.
-We do not currently have good, up-to-date documentation about the
-primitives, perhaps because they are mainly intended for internal use.
-There used to be a long section about them here in the User Guide, but it
-became out of date, and wrong information is worse than none.
-
-The Real Truth about what primitive types there are, and what operations
-work over those types, is held in the file
-compiler/prelude/primops.txt.pp.
-This file is used directly to generate GHC's primitive-operation definitions, so
-it is always correct! It is also intended for processing into text.
-
-Indeed,
-the result of such processing is part of the description of the
- External
- Core language.
-So that document is a good place to look for a type-set version.
-We would be very happy if someone wanted to volunteer to produce an XML
-back end to the program that processes primops.txt so that
-we could include the results here in the User Guide.
-
-What follows here is a brief summary of some main points.
+All these primitive data types and operations are exported by the
+library GHC.Prim, for which there is
+detailed online documentation.
+(This documentation is generated from the file compiler/prelude/primops.txt.pp.)
+
+
+If you want to mention any of the primitive data types or operations in your
+program, you must first import GHC.Prim to bring them
+into scope. Many of them have names ending in "#", and to mention such
+names you need the extension ().
+
+
+The primops make extensive use of unboxed types
+and unboxed tuples, which
+we briefly summarise here. Unboxed types
@@ -366,26 +401,15 @@ would use in C: <literal>Int#</literal> (long int),
know and love—usually one instruction.
</para>
-<para> For some primitive types we have special syntax for literals.
-Anything that would be an integer lexeme followed by a
-<literal>#</literal> is an <literal>Int#</literal> literal, e.g.
-<literal>32#</literal> and <literal>-0x3A#</literal>. Likewise,
-any non-negative integer literal followed by
-<literal>##</literal> is a <literal>Word#</literal> literal.
-Likewise, any floating point literal followed by a
-<literal>#</literal> is a <literal>Float#</literal> literal, and
-followed by <literal>##</literal> is a
-<literal>Double#</literal>. Finally, a string literal followed by a
-<literal>#</literal>, e.g. <literal>"foo"#</literal>,
-is a <literal>Addr#</literal> literal.
-</para>
-
<para>
Primitive (unboxed) types cannot be defined in Haskell, and are
therefore built into the language and compiler. Primitive types are
always unlifted; that is, a value of a primitive type cannot be
-bottom. We use the convention that primitive types, values, and
-operations have a <literal>#</literal> suffix.
+bottom. We use the convention (but it is only a convention)
+that primitive types, values, and
+operations have a <literal>#</literal> suffix (see <xref linkend="magic-hash"/>).
+For some primitive types we have special syntax for literals, also
+described in the <link linkend="magic-hash">same section</link>.
</para>
<para>
@@ -562,8 +586,40 @@ Indeed, the bindings can even be recursive.
<sect1 id="syntax-extns">
<title>Syntactic extensions
+
+ The magic hash
+ The language extension allows "#" as a
+ postfix modifier to identifiers. Thus, "x#" is a valid variable, and "T#" is
+ a valid type constructor or data constructor.
+
+ The hash sign does not change sematics at all. We tend to use variable
+ names ending in "#" for unboxed values or types (e.g. Int#),
+ but there is no requirement to do so; they are just plain ordinary variables.
+ Nor does the extension bring anything into scope.
+ For example, to bring Int# into scope you must
+ import GHC.Prim (see );
+ the extension
+ then allows you to refer to the Int#
+ that is now in scope.
+ The also enables some new forms of literals (see ):
+
+ 'x'# has type Char#
+ "foo"# has type Addr#
+ 3# has type Int#. In general,
+ any Haskell 98 integer lexeme followed by a # is an Int# literal, e.g.
+ -0x3A# as well as 32#.
+ 3## has type Word#. In general,
+ any non-negative Haskell 98 integer lexeme followed by ##
+ is a Word#.
+ 3.2# has type Float#.
+ 3.2## has type Double#
+
+
+
+
+
Hierarchical Modules
@@ -1691,9 +1747,12 @@ to be written infix, very much like expressions. More specifically:
Liberalised type synonyms
-Type synonyms are like macros at the type level, and
+Type synonyms are like macros at the type level, but Haskell 98 imposes many rules
+on individual synonym declarations.
+With the extension,
GHC does validity checking on types only after expanding type synonyms.
-That means that GHC can be very much more liberal about type synonyms than Haskell 98:
+That means that GHC can be very much more liberal about type synonyms than Haskell 98.
+
You can write a forall (including overloading)
in a type synonym, thus:
@@ -1710,7 +1769,8 @@ in a type synonym, thus:
-You can write an unboxed tuple in a type synonym:
+If you also use ,
+you can write an unboxed tuple in a type synonym:
type Pr = (# Int, Int #)
@@ -6674,15 +6734,7 @@ data S = S {-# UNPACK #-} !Int {-# UNPACK #-} !Int
The programmer can specify rewrite rules as part of the source program
-(in a pragma). GHC applies these rewrite rules wherever it can, provided (a)
-the flag () is on,
-and (b) the flag
-() is not specified, and (c) the
- ()
-flag is active.
-
-
-
+(in a pragma).
Here is an example:
@@ -6802,17 +6854,40 @@ variables it mentions, though of course they need to be in scope.
- Rules are automatically exported from a module, just as instance declarations are.
+ All rules are implicitly exported from the module, and are therefore
+in force in any module that imports the module that defined the rule, directly
+or indirectly. (That is, if A imports B, which imports C, then C's rules are
+in force when compiling A.) The situation is very similar to that for instance
+declarations.
+
+
+
+
+
+
+Inside a RULE "forall" is treated as a keyword, regardless of
+any other flag settings. Furthermore, inside a RULE, the language extension
+ is automatically enabled; see
+.
+
+
+Like other pragmas, RULE pragmas are always checked for scope errors, and
+are typechecked. Typechecking means that the LHS and RHS of a rule are typechecked,
+and must have the same type. However, rules are only enabled
+if the flag is
+on (see ).
+
+
-
+Semantics
@@ -6820,9 +6895,17 @@ From a semantic point of view:
-
-Rules are only applied if you use the flag.
+Rules are enabled (that is, used during optimisation)
+by the flag.
+This flag is implied by , and may be switched
+off (as usual) by .
+(NB: enabling without
+may not do what you expect, though, because without GHC
+ignores all optimisation information in interface files;
+see , .)
+Note that is an optimisation flag, and
+has no effect on parsing or typechecking.
@@ -6839,14 +6922,6 @@ expression by substituting for the pattern variables.
- The LHS and RHS of a rule are typechecked, and must have the
-same type.
-
-
-
-
-
-
GHC makes absolutely no attempt to verify that the LHS and RHS
of a rule have the same meaning. That is undecidable in general, and
infeasible in most interesting cases. The responsibility is entirely the programmer's!
@@ -6939,17 +7014,6 @@ pragma on f, to ensure
that it is not inlined until its RULEs have had a chance to fire.
-
-
-
- All rules are implicitly exported from the module, and are therefore
-in force in any module that imports the module that defined the rule, directly
-or indirectly. (That is, if A imports B, which imports C, then C's rules are
-in force when compiling A.) The situation is very similar to that for instance
-declarations.
-
-
-