- Second pass on implementation of let pattern. Parse "let ' par [as x]?

  [in I] := t [return pred] in b", just as SSReflect does with let:. 
  Change implementation: no longer a separate AST node, just add a case_style
  annotation on Cases to indicate it (if ML was dependently typed we
  could ensure that LetPatternStyle Cases have only one term to be
  matched and one branch, alas...). This factors out most code and we lose
  no functionality (win ! win !). Add LetPat.v test suite.

- Slight improvement of inference of return clauses for dependent
  pattern matching. If matching a variable of non-dependent type
  under a tycon that mentions it while giving no return clause, the
  dependency will be automatically infered. Examples at the end of
  DepPat. Should get rid of most explicit returns under tycons.


git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@10727 85f007b7-540e-0410-9357-904b9bb8a0f7

1 files changed, 55 insertions, 0 deletions

diff --git a/test-suite/success/LetPat.v b/test-suite/success/LetPat.v
new file mode 100644
index 0000000000..72c7cc1553
--- /dev/null
+++ b/test-suite/success/LetPat.v
@@ -0,0 +1,55 @@
+(* Simple let-patterns *)
+Variable A B : Type.
+
+Definition l1 (t : A * B * B) : A := let '(x, y, z) := t in x.
+Print l1.
+Definition l2 (t : (A * B) * B) : A := let '((x, y), z) := t in x.
+Definition l3 (t : A * (B * B)) : A := let '(x, (y, z)) := t in x.
+Print l3.
+
+Record someT (A : Type) := mkT { a : nat; b: A }.
+
+Definition l4 A (t : someT A) : nat := let 'mkT x y := t in x.
+Print l4.
+Print sigT.
+
+Definition l5 A (B : A -> Type) (t : sigT B) : B (projT1 t) := 
+  let 'existT x y := t return B (projT1 t) in y.
+
+Definition l6 A (B : A -> Type) (t : sigT B) : B (projT1 t) := 
+  let 'existT x y as t' := t return B (projT1 t') in y.
+
+Definition l7 A (B : A -> Type) (t : sigT B) : B (projT1 t) := 
+  let 'existT x y as t' in sigT _ := t return B (projT1 t') in y.
+
+Definition l8 A (B : A -> Type) (t : sigT B) : B (projT1 t) := 
+  match t with
+    existT x y => y
+  end.
+
+(** An example from algebra, using let' and inference of return clauses
+   to deconstruct contexts. *)
+
+Record a_category (A : Type) (hom : A -> A -> Type) := {  }.
+
+Definition category := { A : Type & { hom : A -> A -> Type & a_category A hom } }.
+
+Record a_functor (A : Type) (hom : A -> A -> Type) (C : a_category A hom) := {  }.
+
+Notation " x :& y " := (@existT _ _ x y) (right associativity, at level 55) : core_scope.
+
+Definition functor (c d : category) :=
+  let ' A :& homA :& CA := c in
+  let ' B :& homB :& CB := d in
+    A -> B.
+
+Definition identity_functor (c : category) : functor c c :=
+  let 'A :& homA :& CA := c in
+    fun x => x.
+
+Definition functor_composition (a b c : category) : functor a b -> functor b c -> functor a c := 
+  let ' (A :& homA :& CA) := a in
+  let ' (B :& homB :& CB) := b in
+  let ' (C :& homB :& CB) := c in
+    fun f g => 
+      fun x : A => g (f x).