* 'master' of https://git.cduce.org/cduce:
  added code for patricia trees
  Added few twisted examples

* debug-typechecking-issue-27-for-merge:
  Remove debugging code.
  Add patricia.cd file from Issue #21
  Check constraints on monomorphic variables at the right place.
  Fix a pretty printing error for ground types (the negative part was not shown due to "worth_complement" being called twice).
  Rework the type variable infrastructure. Remove it from the type structure and have the auxiliary function cache the results as needed.
  Debugging annotations.

Fix a pretty printing error for ground types (the negative part was not shown due to "worth_complement" being called twice).

Fix a pretty printing error for ground types (the negative part was not shown due to "worth_complement" being called twice).

* new-variables-issue-26:
  Rework the type variable infrastructure. Remove it from the type structure and have the auxiliary function cache the results as needed.
  Properly check constraints on monomprhic variable during constraint generation: when a constraint 'a < t or t < 'a with 'a being monomorphic occurs during constraint generation, we check whether it holds for all 'a, that is we use plain subtyping. (It generalizes the fact that 'a < Any or Empty < 'a hold for monomorphic variables, but also accounts for constraints such as 'a < 'a | t and so on).

Conflicts:
	types/types.ml

Rework the type variable infrastructure. Remove it from the type structure and have the auxiliary function cache the results as needed.

when a constraint 'a < t or t < 'a with 'a being monomorphic occurs during constraint generation, we check whether
it holds for all 'a, that is we use plain subtyping.
(It generalizes the fact that 'a < Any or Empty < 'a hold for monomorphic variables, but also accounts for constraints such as 'a < 'a | t and so on).

- Change the precedence of the XML constructor to be stronger than the set-theoretic operations (compatibility with previous CDuce)
- Pretty-printing of regular expressions. When the input type contains a sequence type, print the sequence as a regular expression. Do not print empty sequences unless the rest of the atom components is finite:
     `a |`b | `nil
will be printed as
     [] | `a | `b
but
     Atom \ 'a
will be printed as
     Atom \'a
and not
     Atom \ ('a | `nil) | []
- Remove Arrow from positive arrow part (unless it is the only component)
- Fix a bug where records would be printed instead of attributes

- Simplify the pretty-printing descriptor type
- Fix a bug where some unions were shown as intersections
- Correctly display parentheses where needed (issue: #17)
- Prevent sharing for "small" subtrees (AST less than 6 nodes), so:
  (Int -> Int) -> Int -> Int
  is not shown as:
  X1 -> X1 where X1 = Int -> Int
  (but bigger types are).

Partial fix for issue #20. In the Value.t type, the Concat _ value and the Pair value must have the same underlying representation (since their tag is mutated).
This actually also corrects a bug: Concat _ nodes acts as constructor (like pairs, xml, records, …) and should also be decorated with a sigma. Adding a sigma component to Concat make the segfault disapear. However, for the moment substitutions in Concat are never used.

distribute it (redudantly) under all variables to simplify their pretty-printing.

Hence, instead of having e.g. :

('a \ (Int)) | Char | Int | Atom)

we have
('a | Char | Int | Atom)

* 'master' of https://git.cduce.org/cduce:
  [MINOR] Remove dependence with Str module in parser
  Add syntactic sugar for if_then:
  Bugfix in parser: syntactic sugar if_then_else

Refresh the type of variables in the environement to avoid clash with variables of the interface of the function being typed.

	if cond then expr <=> if cond then expr else []

Note that in case of ambiguity the "else" statement is part of the last "if"
statement:

	if a then if b then c else d <=> if a then (if b then c else d)

Only use the old typing of applications for ground types (not types with only monomorphic variables)