TODO LIST

For more information on any of these issues, contact mercury@cs.mu.oz.au.

syntax

• Warn about the use of the deprecated old-style lambda expressions.

type system

• Fix the three known type inference bugs (see comments in typecheck.m).

mode analysis

• fix various bugs in mode inference: need to fix it to work properly in the presence of functions; also need to change normalise_inst so that it handles complicated insts such as `list_skel(any)'.
• extend the mode system to allow known aliasing. This is needed to make partially instantiated modes and unique modes work. [being done by bromage, nearly finished]
• report an error if two mode declarations for a predicate specify identical modes.
• detect incorrect usage of `bound(...)' insts. That is, make sure that all of the functors in a bound(...) inst are valid functors for the type.

determinism analysis

• add functionality for promise ex declarations:
  • add error checking and type checking as for assertions
  • include declaration information in the module_info
  • take into account mutual exclusivity from promise_exclusive and promise_exclusive_exhaustive declarations during switch detection
  • take into account exhaustiveness from promise_exhaustive and promise_exclusive_exhaustive declarations during determinism analysis

unique modes

• handle nested unique modes
• we will probably need to extend unique modes a bit, in as-yet-unknown ways; need more experience here

module system

• check that the interface for a module is type-correct independently of any declarations or imports in the implementation section
• there are some problems with nested modules (see the language reference manual)

C interface

• exporting things for manipulating Mercury types from C
• better support for types defined in C
• need to deal with memory management issues

code generation

• take advantage of unique modes to do compile-time garbage collection and structure reuse.

WISH LIST

type-system

• allow explicit type qualifications `X : Type' [already done, but need to change module qualifier op to `.' first]
• allow std_util:construct/4 to work for existential types
• remove limitation that higher-order terms are monomorphic. i.e. allow universal quantifiers at the top level of higher-order types, e.g. :- pred foo(all [T] pred(T))..
• constructor classes
• allow a module exporting an abstract type to specify that other modules should not be allowed to test two values of that type for equality (similar to Ada's limited private types). This would be useful for e.g. sets represented as unordered lists with possible duplicates. [this is a subset of the functionality of type classes]
• subtypes?
• optimisation of type representation and manipulation (possibly profiler guided)
• fold/unfolding of types

mode analysis

• split construct/deconstruct unifications into their atomic "micro-unification" pieces when necessary. (When is it necessary?)
• 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?)
• implement `willbe(Inst)' insts, for parallelism
• mode segments & high-level transformation of circularly moded programs.

determinism analysis:

• propagate information about bindings from the condition of an if-then-else to the else so that

  	(if X = [] then .... else X = [A|As], ...)
  

  is considered det.
• turn chains of if-then-elses into switchs where possible. [done by fjh, but not committed; zs not convinced that this is a good idea]

higher-order preds:

• implement single-use higher-order predicate modes. Single-use higher-order predicates would be allowed to bind curried arguments, and to have unique modes for curried arguments.
• allow taking the address of a predicate with multiple modes
• improve support for higher-order programming, eg. by providing operators in the standard library which do things like:
  • compose functions
  • take a predicate with one output argument and treat it like a function. ie. :- func (pred(T)) = T.

module system:

• produce warnings for implementation imports that are not needed
• produce warnings for imports that are in the wrong place (in the interface instead of the implementation, and vice versa) [vice versa done by stayl]

code generation:

• use floating point registers
• allow floating point fields of structures without boxing (need multi-word fields)
• inter-procedural register allocation
• stack allocation of structures
• retarget code generator to Java VM

source-level transformations

• more work on module system, separate compilation, and the multiple specialisation problem
• extended DCGs
• transform non-tail-recursive predicates into tail-recursive form using accumulators [being worked on by petdr]
• improvements to deforestation / partial deduction

low-level optimizations

• reduce the overhead of higher-order predicate calls (avoid copying the real registers into the fake_reg array and back)
• tail recursion optimization using pass-by-reference argument conventions [being worked on by dmo]
• other specializations, e.g. if argument is known to be bound to f(X,Y), then just pass X and Y in registers
• trim stack frames before making recursive calls, to minimize stack usage (this would probably be a pessimization much of the time - zs) and to minimize unnecessary garbage retention.

compilation speed

• improve efficiency of the expansion of equivalence types (currently O(N^2)) (e.g. this is particularly bad when compiling live_vars.m).
• improve efficiency of the module import handling (currently O(N^2))
• improve the efficiency of mode checking very large facts (e.g. this is particularly bad when compiling eliza.m).

better diagnostics

• optional warning for any implicit quantifiers whose scope is not the entire clause (the "John Lloyd" option :-).
• give a better error message for the use of if-then without else.
• give a better error message for the use of `<=' instead of `=<' (but how?)
• give a better error message for type errors involving higher-order pred constants (requested by Bart Demoen)
• give better error messages for syntax errors in lambda expressions

general

• coroutining and parallel versions of Mercury
• implement streams (need coroutining at least)
• implement a very fast turn-around bytecode compiler/interpreter/debugger, similar to Gofer [not-so-fast bytecode compiler done, but bytecode interpreter not implemented]
• implement "accurate" garbage collection
• implement parallel garbage collection
• implement user-defined operators:
  Add a new construct `:- op(Pred, Type, Op).' as in Prolog; change prog_io.m to parse this construct and call io__op accordingly. But how does this fit in with the module system?
• support for easier formal specification translation (eg a Z library, or Z to Mercury).
• improve support for constraint programming
• implement a source visualisation tool
• distributed Mercury
• improved development environment
• additional software engineering tools
  • coverage analysis
  • automatic testing
• literate Mercury
• implement a GUI library (eg Hugs - Fudgets)
• profiling guided optimisations
  • use profiling information to direct linker for optimal code placement (Alpha has a tool for this).
• use of attribute grammar technology (including visit sequence optimization) to implement code with circular modes