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TODO LIST:
----------

write a language reference manual!

improve the users guide

typechecking
------------

- improve error messages for unification of var & functor

- see also wish list comments at the start of typecheck.nl

mode analysis
-------------

- handle "phantom aliasing", i.e. aliasing within a single procedure.
  This is needed to make partially instantiated modes work.

- handle higher-order pred modes

- handle unique modes (some research issues re backtracking)

- detect incorrect usage of `bound(...)' insts.

- handle undefined insts/modes gracefully

- split construct/deconstruct unifications into their atomic
  "micro-unification" pieces when necessary.
  (When is it necessary?)

code generation:
---------------

- generate code for complicated unifies in partially instantiated modes

- generate code for higher-order predicates closures.

- see also comments at the start of modes.nl

general
-------

- tail recursion optimization using pass-by-reference argument conventions

- other specializations, e.g. if argument is known to be bound to
  f(X,Y), then just pass X and Y in registers

- improve efficiency of the implicit quantification pass (currently O(N^2))

- improve efficiency of the module import handling (currently O(N^2))

- {type,mode}check and generate code for solutions/2.

- {type,mode}check and generate code for "lambda" expressions.

- renaming apart of different occurences
  of the same variable; warning about variables which occur in
  overlapping scopes.

- optimization of various sorts

- Combining heap pointer increments in straight-line code into
  a single increment (should be part of value number)

- garbage collection

mercury_to_goedel.nl
--------------------

- see comments at the start of that file

module system
-------------

- check that the interface for a module is type-correct
  independently of any declarations or imports in the implementation
  section

- handle module qualifiers properly

- imports should not be transitive
  (currently we get this right for predicates, constants, and functors,
  but wrong for types, insts, and modes).

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WISH LIST
---------

mode analysis:
--------------

- handle polymorphic modes (some research issues?)

- handle abstract insts in the same way abstract types are handled (a research
  issue - is this possible at all?)

code generation:
----------------

- The generated code should include some profiling hooks.
  In particular, we should add a version of the heap allocation
  macro which takes an extra string parameter identifying which
  routine allocated the memory.  Then we can do heap-allocation
  profiling to identify which routines use up all the bloody memory.

- We could still generate better code for switches

general
-------

- if-then-else and quantification: currently in
	(if
		some [V] P
	then
		Q
	else
		R
	)
   the scope of V is P and Q, not just P.  This is counter-intuitive.
   We should probably require people to write `if_some' rather than
   `if some' to get that effect.  (No obvious similar solution for
   `(some [V] P -> Q ; R)', unfortunately.)

- switch detection: handle multi-level indexing (cse)

- more work on module system, separate compilation, and the multiple
  specialization problem

- deforestation

- mode segments & high-level transformation of circularly moded programs.

- implement user-defined operators:
	Add a new construct `:- op(Pred, Type, Op).' as in Prolog;
	change prog_io.nl to parse this construct and call io__op
	accordingly.

- optional warning for any implicit quantifiers whose scope is not
  the entire clause (the "John Lloyd" option :-).

- warn about multiple calls to a predicate with the same input arguments,
  because this is likely to be a programming mistake.
  eg.

	p(...) :-
		...
		q(InA, InB, OutC, OutD),
		...
		q(InA, InB, OutE, OutF).

  should result in

	Warning: redundant call to `q(InA, InB, _, _)'

- issue a warning if the only use of an argument is in a recursive call

- better error handling

- fix all the `XXX's, `xxx's, `YYY's and `%%%'s.

- implement a debugger and a profiler

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