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Estimated hours taken: 70 (plus whatever pets spent when he wrote the original version of this) This change adds a new extras directory, "references". This directory contains two impure reference type modules and a module that allows scoped non-backtrackable update, along with examples of using them and tests. These modules are intended to be useful when HAL is retargetted to Mercury, for implementing global variables (backtracking and non-backtracking), and may also be useful for the debugger. In order to implement these features, a new memory zone "global heap" was added to the runtime system, for a heap which is not reclaimed on failure, along with a pair of functions for copying terms to this heap. runtime/mercury_deep_copy.c: runtime/mercury_deep_copy.h: Added two functions, MR_make_permanent() and MR_make_partially_permanent(), which essentially do a deep copy of a term to the global heap. (In conservative GC grades, these functions actually do nothing). runtime/mercury_engine.c: runtime/mercury_engine.h: Added fields global_heap_zone and e_global_hp (for the global heap and its heap pointer) to the MR_mercury_engine_struct, along with appropriate initialisation, etc. Defined MR_heap_zone, MR_solutions_heap_zone, and MR_global_heap_zone for convenient access to the corresponding field of the relevant Mercury engine. runtime/mercury_memory.c: Added code for handling the size and zone size of the global heap. runtime/mercury_regorder.h: runtime/mercury_regs.h: Defined MR_global_hp (the global heap pointer for general use), along with corresponding other changes. runtime/mercury_wrapper.c: runtime/mercury_wrapper.h: Added declarations and initialisation of the size and zone_size of the global_heap. Added an entry for MR_GLOBAL_HP_RN to print_register_usage_counts() (plus missing entries for MR_SOL_HP_RN, MR_MIN_HP_REC and MR_MIN_SOL_HP_REC). New files: extras/references/Mmakefile: Mmakefile for building and testing these modules. extras/references/README: Description of contents of this directory. extras/references/global.m: A wrapper module for building a library containing the nb_reference, reference and scoped_update modules. extras/references/nb_reference.m: Implements references which are not backtracked on failure. extras/references/reference.m: Implements references which *are* backtracked on failure. extras/references/scoped_update.m: Allows nested scoping of non-backtracking references. extras/references/samples/Mmakefile: extras/references/samples/max_of.m: extras/references/samples/max_test.exp: extras/references/samples/max_test.m: An example of using a non-backtracking reference (to find the maximum of the solutions generated by a predicate), with tests. extras/references/tests/Mmakefile: extras/references/tests/ref_test.exp: extras/references/tests/ref_test.m: Some tests of references (backtracking and non-backtracking) and scoping.
This directory contains two impure reference type modules, and a module that allows scoped non-backtrackable update, plus two example modules using these types. These serve as an example of impure coding. Generally this sort of coding is not necessary, and it can be quite tedious and error-prone, but occasionally it may permit greater efficiency than using pure Mercury code, or may permit you to write in Mercury what you would otherwise have to write in C. See section 12.2 of the Mercury Language References Manual for more information on impurity. This directory contains reference.m a backtrackable reference types nb_reference.m a non-backtrackable reference types scoped_update.m scoping for non-backtrackable updates global.m a wrapper module used for building a library containing the above modules The samples directory contains max_of.m an example of non-backtrackable references test_max.m test case for max_of.m The tests directory contains test_refs.m tests of reference.m, nb_reference.m and scoped_update.m