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diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index fb2124e..d9a6198 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -964,7 +964,7 @@ a data type with no constructors. For example:
Syntactically, the declaration lacks the "= constrs" part. The
type can be parameterised over types of any kind, but if the kind is
not * then an explicit kind annotation must be used
-(see ).
+(see ).
Such data types have only one value, namely bottom.
Nevertheless, they can be useful when defining "phantom types".
@@ -1226,7 +1226,7 @@ that collection of packages in a uniform manner. You can express
quite a bit of object-oriented-like programming this way.
-
+Why existential?
@@ -1249,9 +1249,9 @@ But Haskell programmers can safely think of the ordinary
adding a new existential quantification construct.
-
+
-
+Type classes
@@ -1311,9 +1311,9 @@ Notice the way that the syntax fits smoothly with that used for
universal quantification earlier.
-
+
-
+Record Constructors
@@ -1330,7 +1330,7 @@ data Counter a = forall self. NewCounter
Here tag is a public field, with a well-typed selector
function tag :: Counter a -> a. The self
type is hidden from the outside; any attempt to apply _this,
-_inc or _output as functions will raise a
+_inc or _display as functions will raise a
compile-time error. In other words, GHC defines a record selector function
only for fields whose type does not mention the existentially-quantified variables.
(This example used an underscore in the fields for which record selectors
@@ -1376,10 +1376,10 @@ setTag obj t = obj{ tag = t }
-
+
-
+Restrictions
@@ -1530,7 +1530,7 @@ declarations. Define your own instances!
-
+
@@ -2546,7 +2546,7 @@ the context and head of the instance declaration can each consist of arbitrary
following rules:
-For each assertion in the context:
+The Paterson Conditions: for each assertion in the context
No type variable has more occurrences in the assertion than in the headThe assertion has fewer constructors and variables (taken together
@@ -2554,7 +2554,7 @@ For each assertion in the context:
-The coverage condition. For each functional dependency,
+The Coverage Condition. For each functional dependency,
tvsleft->tvsright, of the class,
every type variable in
@@ -2566,11 +2566,15 @@ corresponding type in the instance declaration.
These restrictions ensure that context reduction terminates: each reduction
step makes the problem smaller by at least one
-constructor. For example, the following would make the type checker
-loop if it wasn't excluded:
-
- instance C a => C a where ...
-
+constructor. Both the Paterson Conditions and the Coverage Condition are lifted
+if you give the
+flag ().
+You can find lots of background material about the reason for these
+restrictions in the paper
+Understanding functional dependencies via Constraint Handling Rules.
+
+
For example, these are OK:
instance C Int [a] -- Multiple parameters
@@ -2622,11 +2626,6 @@ something more specific does not:
op = ... -- Default
-You can find lots of background material about the reason for these
-restrictions in the paper
-Understanding functional dependencies via Constraint Handling Rules.
-
@@ -2691,8 +2690,8 @@ makes instance inference go into a loop, because it requires the constraint
Nevertheless, GHC allows you to experiment with more liberal rules. If you use
the experimental flag
-fallow-undecidable-instances
-option, you can use arbitrary
-types in both an instance context and instance head. Termination is ensured by having a
+option, both the Paterson Conditions and the Coverage Condition
+(described in ) are lifted. Termination is ensured by having a
fixed-depth recursion stack. If you exceed the stack depth you get a
sort of backtrace, and the opportunity to increase the stack depth
with N.
@@ -3372,7 +3371,7 @@ and you'd be right. That is why they are an experimental feature.
================ END OF Linear Implicit Parameters commented out -->
-
+Explicitly-kinded quantification
@@ -3492,7 +3491,6 @@ including an operational type class context, is legal:
On the left or right (see f4, for example)
of a function arrow
- On the right of a function arrow (see ) As the argument of a constructor, or type of a field, in a data type declaration. For
example, any of the f1,f2,f3,g1,g2 above would be valid
field type signatures.
@@ -4087,15 +4085,39 @@ The class IsString is defined as:
class IsString a where
fromString :: String -> a
-And the only predefined instance is the obvious one to make strings work as usual:
+The only predefined instance is the obvious one to make strings work as usual:
instance IsString [Char] where
fromString cs = cs
+The class IsString is not in scope by default. If you want to mention
+it explicitly (for exmaple, to give an instance declaration for it), you can import it
+from module GHC.Exts.
+
+
+Haskell's defaulting mechanism is extended to cover string literals, when is specified.
+Specifically:
+
+
+Each type in a default declaration must be an
+instance of Numor of IsString.
+
+
+
+The standard defaulting rule (Haskell Report, Section 4.3.4)
+is extended thus: defaulting applies when all the unresolved constraints involve standard classes
+orIsString; and at least one is a numeric class
+orIsString.
+
+
A small example:
+module Main where
+
+import GHC.Exts( IsString(..) )
+
newtype MyString = MyString String deriving (Eq, Show)
instance IsString MyString where
fromString = MyString
@@ -4227,8 +4249,8 @@ Tim Sheard is going to expand it.)
- Furthermore, the you can only run a function at compile time if it is imported
- from another module that is not part of a mutually-recursive group of modules
+ Furthermore, you can only run a function at compile time if it is imported
+ from another module that is not part of a mutually-recursive group of modules
that includes the module currently being compiled. For example, when compiling module A,
you can only run Template Haskell functions imported from B if B does not import A (directly or indirectly).
The reason should be clear: to run B we must compile and run A, but we are currently type-checking A.
@@ -4853,7 +4875,7 @@ Because the preprocessor targets Haskell (rather than Core),
-
+Bang patterns
Bang patterns
@@ -4868,7 +4890,7 @@ than the material below.
Bang patterns are enabled by the flag .
-
+Informal description of bang patterns
@@ -4923,7 +4945,7 @@ is part of the syntax of let bindings.
-
+Syntax and semantics
@@ -4997,7 +5019,7 @@ a module.
-
+Assertions
Assertions