existing-records.md

@@ -23,62 +23,111 @@ This would make the update syntax actually useful
 
 - label-based pattern matching
 
-
-the function:
-
-
-```wiki
-  f val { x = "foo" } = 4
-```
-
-
-should match if passed a Foo or a Bar with x being equal to "foo" and val would be bound to its argument (like an @ pattern)
+>
+> >
+> >
+> > the function:
+> >
+> >
+> > ```wiki
+> >   f val { x = "foo" } = 4
+> > ```
+> >
+> >
+> > should match if passed a Foo or a Bar with x being equal to "foo" and val would be bound to its argument (like an @
+> >
+> >
+>
+
+
+pattern)
 
 
 ```wiki
  g _ { y = 3 } = 4
 ```
 
-
-would match only the Bar constructor since it is the only one with a  y field.
-
-
-
-This would mitigate the problems caused by accessors being partial functions since you can use a simple case statement to get the effect of an accesor that returns its result in a Maybe.
-
-
-
-Note from Simon.  I hate that the above defn of 'f' has just one argument (val {x="foo")), 
-whereas it looks as if it has two.  (This is a problem with existing Haskell.)  It looks
-like 'f' has an argument 'val' and another arguement that is a free-standing record, 
-something we really want in the end anyhow.  Not sure how to fix this.  val@{x="foo")?
-
+>
+>
+> would match only the Bar constructor since it is the only one with a  y field.
+>
+>
+
+>
+>
+> This would mitigate the problems caused by accessors being partial functions since you can use a simple case statement to get the effect of an accesor that returns its result in a Maybe.
+>
+>
+
+>
+>
+> Note from Simon.  I hate that the above defn of 'f' has just one argument (val {x="foo")), 
+> whereas it looks as if it has two.  (This is a problem with existing Haskell.)  It looks
+> like 'f' has an argument 'val' and another arguement that is a free-standing record, 
+> something we really want in the end anyhow.  Not sure how to fix this.  val@{x="foo")?
+>
+>
 
 - first class update and setting syntax (more advanced, needs better syntax)
 
-
-A syntax for updating and setting fields should be allowed.
-
-
-
-some possibilites are 
-
+>
+> >
+> >
+> > A syntax for updating and setting fields should be allowed.
+> >
+> >
+>
+
+>
+> >
+> >
+> > some possibilites are 
+> >
+> >
+>
 
 ```wiki
 
 foo { x = }
 
-would be equivalant to (\v -> foo { x = v })
+would be equivalent to (\v -> foo { x = v })
 
 foo { x \ }
 
-would be equivalant to 
+would be equivalent to 
 
 (\f -> foo { x = case foo of _ {x} -> foo { x = f x }; _ -> foo }) 
 
-
 ```
 
+- polymorphic record update
+
+>
+> >
+> >
+> > Given a record like:
+> >
+> >
+> > ```wiki
+> > data Foo a = Foo { bar :: a }
+> > ```
+> >
+> >
+> > it would be nice to be able to update it like:
+> >
+> >
+> > ```wiki
+> > f = Foo { bar = 'a' }
+> > g = f { bar = False }
+> > ```
+> >
+> >
+> > Note the change in the type of the stored field.  At the moment, such a record update must be written using the
+> > data constructor, not the update syntax.
+> >
+> >
+>
+
 ## open statement
 
 
@@ -108,3 +157,7 @@ f x = ... where
 open x would be allowed at the top level, in a let binding, or in a where binding.
 
 
+
+  
+
+