├── .gitignore ├── LICENSE ├── README.md ├── dev.pl ├── pack.pl ├── prolog ├── mavis.pl └── readme.txt ├── t ├── determinism.pl ├── intersection.pl ├── predicates.pl └── subtypes.pl └── test.pl /.gitignore: -------------------------------------------------------------------------------- 1 | *~ 2 | doc/ 3 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU LESSER GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright © 2007 Free Software Foundation, Inc. 5 | 6 | Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 7 | 8 | This version of the GNU Lesser General Public License incorporates the terms and conditions of version 3 of the GNU General Public License, supplemented by the additional permissions listed below. 9 | 10 | 0. 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Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. 53 | 54 | Each version is given a distinguishing version number. If the Library as you received it specifies that a certain numbered version of the GNU Lesser General Public License “or any later version” applies to it, you have the option of following the terms and conditions either of that published version or of any later version published by the Free Software Foundation. If the Library as you received it does not specify a version number of the GNU Lesser General Public License, you may choose any version of the GNU Lesser General Public License ever published by the Free Software Foundation. 55 | 56 | If the Library as you received it specifies that a proxy can decide whether future versions of the GNU Lesser General Public License shall apply, that proxy's public statement of acceptance of any version is permanent authorization for you to choose that version for the Library. -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Synopsis 2 | 3 | :- use_module(library(mavis)). 4 | 5 | %% even(+X:integer) is semidet. 6 | even(X) :- 7 | 0 is X mod 2. 8 | 9 | # Description 10 | 11 | The =mavis= module (because she helps with typing ;-) allows one to 12 | use optional type declarations in Prolog code. During *development*, 13 | these declarations throw informative exceptions when values don't match 14 | types. A typical development environment converts this into a helpful 15 | stack track which assists in locating the error. 16 | 17 | In *production*, the declarations are completely removed by macros 18 | and do nothing. Production time is defined as any time when optimization is enabled: 19 | `current_prolog_flag(optimise, true)`. 20 | 21 | Type declarations can be give manually by calling the/2. `mavis` also inserts 22 | type declarations for you based on your PlDoc structured comments. For 23 | example, during development, the definition of `even` above becomes 24 | 25 | even(A) :- 26 | the(integer, A), 27 | 0 is A mod 2. 28 | 29 | The library also takes into account groundedness and determinsm as 30 | specified in the mode line given to PlDoc. Currently the library recognises 31 | 32 | `erroneous`, `failure`,`semidet`,`det`,`multi`,`nondet` 33 | 34 | The different determinism qualifiers are interpreted as follows: 35 | 36 | * `failure`: 0 solutions 37 | * `semidet`: 0 or 1 solution 38 | * `det`: 1 solution 39 | * `multi`: more than one solution 40 | * `nondet`: Any number of solutions including 0 41 | 42 | The groundedness currently must be one of: 43 | 44 | `++`,`+`,`?`,`--`,`-`,`:`,`@`,`!` 45 | 46 | These are interpreted as follows: 47 | 48 | * `++` means *completely* ground on entry. 49 | * `+` means ground in a way compatible with type declaration. For `any`, 50 | this provides no checkable information. 51 | * `?` means either ground, unground or mixed. If it is not a variable, we will demote the determinism as follows: 52 | - `det` => `semidet` 53 | - `multi` => `nondet` 54 | * `--` means variable input, and type compatible output. 55 | * `-` means an output parameter. The output should be compatible with the type. If it is not a variable, we will demote the determinism as follows: 56 | - `det` => `semidet` 57 | - `multi` => `nondet` 58 | * `:` means a goal. Currently no checking is done. 59 | * `@` means not further bound than on input. Currently no checking is done. 60 | * `!` means side-effectable variable. Currently no checking is done. 61 | 62 | "Compatibility" means that running the double-negated type over the 63 | variable is successful, i.e. the input structure which is defined does 64 | not contradict the type. 65 | 66 | ## Why? 67 | 68 | We love dynamic types. That's one reason we love Prolog. But 69 | sometimes it is useful to distinguish between a failure, and an 70 | incorrect utlisation of the calling contract. Types can: 71 | 72 | * offer documentation to those reading our code 73 | * help find errors during development 74 | * structure our thinking during development 75 | * provide data for static analysis tools 76 | 77 | # Defining new types 78 | 79 | Mavis types are defined using error:has_type/2. We might define an 80 | `even_integer` type with 81 | 82 | error:has_type(even_integer, X) :- 83 | 0 is X mod 2. 84 | 85 | We can use the definition manually: 86 | 87 | frobnify(A, B) :- 88 | the(integer, A), 89 | the(even_integer, B), 90 | B is 2*A. 91 | 92 | or simply add it to our PlDoc comments: 93 | 94 | %% frobnify(+A:integer, -B:even_integer) 95 | frobnify(A, B) :- 96 | B is 2*A. 97 | 98 | We can declare types for bound variables, like `A`, and 99 | not-yet-bound variables, like `B`. The type constraints are implemented 100 | with when/2 so they apply as soon as a variable is ground. 101 | 102 | To disable type checking in production, start Prolog with the 103 | `-O` command line argument. A macro eliminates calls to the/2 so they 104 | have no runtime overhead. 105 | 106 | # Changes in this Version 107 | 108 | * Fix packaging error 109 | * Add determinism checking 110 | * Add groundedness checking 111 | 112 | # TODO 113 | 114 | There should be a less ad-hoc method of mode selection. It would also 115 | be useful to extend the groundedness criteria 116 | 117 | In future versions we hope to incorporate a gradual typing discipline 118 | using abstract interpretation. This could potentially find type, 119 | groundedness and determinacy errors before we have run the 120 | program. Ultimately it may also provide performance improvements. 121 | 122 | It would also be very nice to include polymorphism, however, this 123 | requires that we have some way to select a type. As there is no 124 | principle typing, this is potentially a (very interesting) can of 125 | worms. 126 | 127 | Also of some interest would be dependent type checking, which at least 128 | in the dynamic case, might be tractable. 129 | 130 | # Issues 131 | 132 | When using metapredicates such as maplist, goal expansion will get 133 | confused and generate incorrect clauses unless the predicate has the 134 | appropriate number of arguments. This can be achieved by wrapping the 135 | call in a suitable lambda form. e.g. If p is given a modeline then: 136 | 137 | ``` 138 | maplist(p,Xs,Ys) 139 | ``` 140 | 141 | should be replaced with: 142 | 143 | ``` 144 | maplist([X,Y]>>(p(X,Y)),Xs,Ys 145 | ``` 146 | 147 | # Installation 148 | 149 | Using SWI-Prolog 6.3.16 or later: 150 | 151 | $ swipl 152 | 1 ?- pack_install(mavis). 153 | 154 | Source code available and pull requests accepted on GitHub: 155 | https://github.com/GavinMendelGleason/mavis 156 | 157 | # Authors 158 | 159 | * Michael Hendricks 160 | * Gavin Mendel-Gleason 161 | -------------------------------------------------------------------------------- /dev.pl: -------------------------------------------------------------------------------- 1 | :- debug(mavis). 2 | :- user:asserta(file_search_path(library,prolog)). 3 | :- guitracer. 4 | -------------------------------------------------------------------------------- /pack.pl: -------------------------------------------------------------------------------- 1 | name(mavis). 2 | title('Optional type declarations'). 3 | 4 | version('0.2.3'). 5 | download('http://packs.ndrix.com/mavis/mavis-0.2.3.tgz'). 6 | 7 | keywords([types]). 8 | 9 | requires(list_util). 10 | requires(quickcheck). 11 | 12 | author( 'Michael Hendricks', 'michael@ndrix.org' ). 13 | packager( 'Michael Hendricks', 'michael@ndrix.org' ). 14 | maintainer( 'Michael Hendricks', 'michael@ndrix.org' ). 15 | home('http://packs.ndrix.com/mavis/index.html'). 16 | -------------------------------------------------------------------------------- /prolog/mavis.pl: -------------------------------------------------------------------------------- 1 | :- module(mavis, [ the/2 2 | , has_intersection/2 3 | , has_subtype/2 4 | , known_type/1 5 | , build_type_assertions/3 6 | , build_determinism_assertions/2 7 | , run_goal_at_mode/4 8 | ]). 9 | 10 | 11 | :- use_module(library(quickcheck)). 12 | :- use_module(library(error)). 13 | 14 | 15 | /** Optional type declarations 16 | Declare optional types which are checked during development time. 17 | See pack documentation for more information. 18 | */ 19 | 20 | module_wants_mavis(Module) :- 21 | Module \= mavis, 22 | predicate_property(Module:the(_,_), imported_from(mavis)). 23 | 24 | %% the(+Type:type, ?Value) is det. 25 | % 26 | % Declare that Value has the given Type. 27 | % Succeeds if Value is bound to a value that's compatible 28 | % with Type. Throws an informative exception if Value 29 | % is bound to a value that's not compatible with Type. 30 | % If Value is not bound, the type check is delayed until 31 | % Value becomes ground. 32 | % 33 | % When optimizations are enabled 34 | % (=|current_prolog_flag(optimise, true)|=) a macro removes =the= 35 | % entirely so that it always succeeds. 36 | :- if(current_prolog_flag(optimise,true)). 37 | 38 | the(_,_). % avoid "Exported procedure mavis:the/2 is not defined" 39 | user:goal_expansion(the(_,_), true). 40 | 41 | build_determinism_assertions(_,_) :- fail. 42 | build_type_assertions(_,_,_) :- fail. 43 | run_goal_at_mode(_,_,_,_) :- fail. 44 | 45 | :- else. 46 | 47 | :- use_module(library(apply), [exclude/3]). 48 | :- use_module(library(charsio), [read_term_from_chars/3]). 49 | :- use_module(library(list_util), [xfy_list/3,split_at/4]). 50 | :- use_module(library(pldoc)). 51 | :- use_module(library(pldoc/doc_wiki), [indented_lines/3]). 52 | :- use_module(library(when), [when/2]). 53 | :- doc_collect(true). 54 | 55 | % extract mode declaration from a structured comment 56 | mode_declaration(Comment, ModeCodes) :- 57 | string_to_list(Comment, Codes), 58 | phrase(pldoc_process:structured_comment(Prefixes,_), Codes, _), 59 | indented_lines(Codes, Prefixes, Lines), 60 | pldoc_modes:mode_lines(Lines, ModeCodes, [], _). 61 | 62 | % There may be more varieties of this that we have to handle 63 | % see read_term/2 64 | end_pos(Pos,End) :- 65 | ( Pos=term_position(_, End, _, _, _) 66 | -> true 67 | ; Pos=_-End). 68 | 69 | exhaustive_read_term(Codes,[Term|Terms]) :- 70 | Options = [module(pldoc_modes), 71 | variable_names(Vars), 72 | subterm_positions(Pos)], 73 | read_term_from_chars(Codes,Term,Options), 74 | end_pos(Pos,End), 75 | Term \= end_of_file, 76 | !, 77 | maplist(call,Vars), 78 | Next is End + 2, % one for 0 offset, one for '.' 79 | split_at(Next,Codes,_,NewCodes), 80 | exhaustive_read_term(NewCodes,Terms). 81 | exhaustive_read_term(_Codes,[]). 82 | 83 | % read all mode declarations from character codes 84 | read_mode_declarations(ModeCodes, Modes) :- 85 | exhaustive_read_term(ModeCodes, Modes). 86 | 87 | % convert mode declarations to a standard form 88 | normalize_mode(Mode0, Args, Det) :- 89 | (Mode0 = is(Mode1, Det) -> true; Mode1=Mode0, Det=nondet), 90 | (Mode1 = //(Mode2) -> Slash='//'; Mode2=Mode1, Slash='/' ), 91 | _ = Slash, % avoid singleton warnings (until Slash is needed) 92 | Mode2 =.. [_|RawArgs], 93 | maplist(normalize_args, RawArgs, Args). 94 | 95 | normalize_args(X0, arg(Mode,Name,Type)) :- 96 | ( var(X0) -> X1 = ?(X0:any) ; X1=X0 ), 97 | ( X1 =.. [Mode0,Arg] -> true; Mode0='?', Arg=X1 ), 98 | ( member(Mode0, [++,+,-,--,?,:,@,!]) -> Mode=Mode0; Mode='?' ), 99 | ( nonvar(Arg), Arg=Name:Type -> true; Name=Arg, Type=any). 100 | 101 | the(Type, Value) :- 102 | when(ground(Value), error:must_be(Type, Value)). 103 | 104 | % create a the/2 type assertion based on a variable and 105 | % the declared mode information for that variable. 106 | type_declaration(Var, arg(_,_,Type), the(Type, Var)). 107 | 108 | % convert a clause head into a goal which asserts all types 109 | % associated with that head. Slash is '/' for a normal 110 | % predicate and '//' for a DCG. Pneumonic: foo/1 vs foo//1 111 | build_type_assertions(Slash, Head, TypeGoal) :- 112 | % does this module want mavis type assertions? 113 | prolog_load_context(module, Module), 114 | mavis:module_wants_mavis(Module), 115 | 116 | % fetch this predicate's structured comment 117 | functor(Head, Name, Arity), 118 | Indicator =.. [Slash, Name, Arity], 119 | pldoc_process:doc_comment(Module:Indicator,_,_,Comment), 120 | 121 | % parse and normalize mode description 122 | mode_declaration(Comment, ModeText), 123 | %debug(mavis, "~q has modeline `~s`~n", [Module:Indicator, ModeText]), 124 | % Warning: Potential bug!!! 125 | % We assume type consistency between modes... 126 | %debug(mavis, "~q has modeline `~s`~n", [Module:Indicator, ModeText]), 127 | read_mode_declarations(ModeText, [RawMode|_]), 128 | debug(mavis, "~q has types from `~q`~n", [Module:Indicator, RawMode]), 129 | normalize_mode(RawMode, ModeArgs, _Determinism), 130 | 131 | Head =.. [Name|HeadArgs], 132 | maplist(type_declaration, HeadArgs, ModeArgs, AllTypes), 133 | exclude(=@=(the(any, _)), AllTypes, Types), 134 | xfy_list(',', TypeGoal, Types). 135 | 136 | build_determinism_assertions(Goal,Wrapped) :- 137 | % does this module want mavis type assertions? 138 | prolog_load_context(module, Module), 139 | mavis:module_wants_mavis(Module), 140 | 141 | % fetch this predicate's structured comment 142 | functor(Goal, Name, Arity), 143 | Indicator =.. ['/', Name, Arity], 144 | 145 | pldoc_process:doc_comment(Module:Indicator,_,_,Comment), 146 | 147 | % parse and normalize mode description 148 | mode_declaration(Comment, ModeText), 149 | read_mode_declarations(ModeText, RawModes), 150 | % fail if there are no mode declarations (to leave the goal unchanged) 151 | \+ RawModes = [], 152 | maplist([RawMode,mode(ModeArgs,Determinism)]>>normalize_mode(RawMode, ModeArgs, Determinism), 153 | RawModes,Modes), 154 | %%debug(mavis, "~q has modeline `~s`~n", [Module:Indicator, Modes]), 155 | % We should really check for mode consistency here. 156 | 157 | Goal =.. [Name|Args], 158 | Wrapped = mavis:run_goal_at_mode(Module,Name,Modes,Args). 159 | 160 | % pre_check_groundedness(arg(Groundedness,_,Type),Arg,Demote) is det. 161 | % Promote holds a 0 or 1 depending on whether we should demote 162 | % in the event of increased nondeterminism. 163 | pre_check_groundedness(arg('++',_,Type),Arg,0) :- 164 | ground(Arg), 165 | ( \+ error:has_type(Type,Arg) 166 | -> throw(domain_error(Type,Arg)) 167 | ; true). 168 | pre_check_groundedness(arg('+',_,Type),Arg,0) :- 169 | % This will be type checked too late due to suspension 170 | % unless we do it now. 171 | % (negation avoids bindings) 172 | \+ var(Arg), 173 | ( \+ error:has_type(Type,Arg) 174 | -> throw(domain_error(Type,Arg)) 175 | ; true). 176 | pre_check_groundedness(arg('-',_,_),Arg,Demote) :- 177 | ( var(Arg) 178 | -> Demote = 0 179 | ; Demote = 1). 180 | pre_check_groundedness(arg('--',_,_),Arg,0) :- 181 | var(Arg). 182 | pre_check_groundedness(arg('?',_,_),Arg,Demote) :- 183 | ( var(Arg) 184 | -> Demote = 0 185 | ; Demote = 1). 186 | pre_check_groundedness(arg(':',_,_),_Arg,0). 187 | pre_check_groundedness(arg('!',_,_),_Arg,0). 188 | pre_check_groundedness(arg('@',_,_),_Arg,0). 189 | 190 | post_check_groundedness(arg('-',_,Type),Arg) :- 191 | !, 192 | ( \+ error:has_type(Type,Arg) 193 | -> throw(domain_error(Type,Arg)) 194 | ; true). 195 | post_check_groundedness(arg('--',_,Type),Arg) :- 196 | !, 197 | ( \+ error:has_type(Type,Arg) 198 | -> throw(domain_error(Type,Arg)) 199 | ; true). 200 | post_check_groundedness(arg(_,_,_),_Arg). 201 | 202 | demote(det,1,semidet). 203 | demote(multi,1,nondet). 204 | demote(fail,1,fail). 205 | demote(semidet,1,semidet). 206 | demote(nondet,1,nondet). 207 | demote(erroneous,1,erroneous). 208 | demote(X,0,X). 209 | 210 | choose_mode([mode(Mode,Determinism)|_Modes],Args,_Module,_Name, 211 | mode(Mode,DeterminismPrime)) :- 212 | maplist(pre_check_groundedness,Mode,Args,DemotionVotes), 213 | foldl([X,Y,R]>>(R is X \/ Y),DemotionVotes,0,Demote), 214 | demote(Determinism,Demote,DeterminismPrime), 215 | !. 216 | choose_mode([_|Modes],Args,Module,Name,Mode) :- 217 | choose_mode(Modes,Args,Module,Name,Mode). 218 | 219 | run_goal_at_mode(Module,Name,Modes,Args) :- 220 | Goal =.. [Name|Args], 221 | ( choose_mode(Modes,Args,Module,Name,mode(Mode,Determinism)) 222 | -> true 223 | ; throw(mode_error(Modes,apply(Module:Name,Args)))), 224 | run_goal_with_determinism(Determinism,Module,Goal), 225 | ( maplist(post_check_groundedness,Mode,Args) 226 | -> true 227 | ; throw(mode_error(Modes,apply(Module:Name,Args)))). 228 | 229 | run_goal_with_determinism(erroneous,Module,Goal) :- 230 | !, 231 | throw(determinism_error(Module:Goal,erroneous)). 232 | run_goal_with_determinism(failure,Module,Goal) :- 233 | !, 234 | call(Module:Goal), 235 | throw(determinism_error(Module:Goal,failure)). 236 | run_goal_with_determinism(det,Module,Goal) :- 237 | !, 238 | ( call_cleanup(Module:Goal, Det=true), 239 | ( Det == true 240 | -> true 241 | ; throw(determinism_error(Module:Goal, det)) 242 | ) 243 | -> true 244 | ; throw(determinism_error(Module:Goal, det)) 245 | ). 246 | run_goal_with_determinism(semidet,Module,Goal) :- 247 | !, 248 | ( call_cleanup(Module:Goal, Det=true), 249 | ( Det == true 250 | -> true 251 | ; throw(determinism_error(Module:Goal, semidet)) 252 | ) 253 | -> true 254 | ; fail 255 | ). 256 | run_goal_with_determinism(multi,Module,Goal) :- 257 | !, 258 | ( call(Module:Goal) 259 | *-> true 260 | ; throw(determinism_error(Module:Goal,multi)) 261 | ). 262 | run_goal_with_determinism(_,Module,Goal) :- 263 | call(Module:Goal). 264 | 265 | bodyless_predicate(Term) :- 266 | \+ Term = (:-_), 267 | \+ Term = (_:-_), 268 | \+ Term = (_-->_), 269 | \+ Term = end_of_file. 270 | 271 | user:term_expansion((Head:-Body), (Head:-TypeGoal,Body)) :- 272 | Slash = '/', 273 | build_type_assertions(Slash, Head, TypeGoal). 274 | 275 | user:term_expansion(Head,(Head:-TypeGoal)) :- 276 | bodyless_predicate(Head), 277 | Slash = '/', 278 | build_type_assertions(Slash, Head, TypeGoal). 279 | 280 | user:term_expansion((Head-->Body), (Head-->{TypeGoal},Body)) :- 281 | Slash = '//', 282 | build_type_assertions(Slash, Head, TypeGoal). 283 | 284 | % TODO: 285 | % We need to check mode assignments and discover if they are 286 | % A) disjoint 287 | % a) if they are disjoint we need to check groundedness 288 | % 1) Add dynamic check groudedness. 289 | % 2) Do a separate determinism check per groudedness. 290 | % b) Throw runtime error if not disjoint. 291 | % 292 | % TODO: 293 | % Later it would be nice if we had skeletons (ala mercury). 294 | user:goal_expansion(Goal,Wrapped) :- 295 | build_determinism_assertions(Goal,Wrapped), 296 | debug(mavis,'~q => ~q~n', [Goal,Wrapped]). 297 | 298 | :- multifile prolog:message//1. 299 | prolog:message(determinism_error(Goal, Det)) --> 300 | [ 'The Goal ~q is not of determinism ~q'-[Goal,Det]]. 301 | prolog:message(domain_error(Domain, Term)) --> 302 | [ 'The term ~q is not in the domain ~q'-[Term,Domain]]. 303 | prolog:message(mode_error(Mode, Term)) --> 304 | [ 'The term ~q does not have a valid mode in ~q'-[Term,Mode]]. 305 | 306 | :- endif. 307 | 308 | 309 | % below here, code that loads all the time 310 | 311 | %% type_subtype(?Type, ?Subtype) 312 | % 313 | % Multifile predicate for declaring that a Type has a Subtype. It 314 | % should only be necessary to add clauses to this predicate if 315 | % has_subtype/2 has trouble deriving this information based on 316 | % your definition of `quickcheck:arbitrary/2`. 317 | :- dynamic type_subtype/2. 318 | :- multifile type_subtype/2. 319 | 320 | %% has_subtype(+Type, +Subtype) is semidet. 321 | % 322 | % True if all values of Subtype are also values of Type. This can be 323 | % used to determine whether arguments of one type can be passed to a 324 | % predicate which demands arguments of another type. 325 | % 326 | % This predicate performs probabilistic subtype detection by leveraging 327 | % your definitions for `error:has_type/2` and `quickcheck:arbitrary/2`. 328 | % If this predicate is not detecting your types correctly, either 329 | % improve your quickcheck:arbitrary/2 definition or add clauses to 330 | % the multifile predicate type_subtype/2. 331 | has_subtype(Type, Subtype) :- 332 | ( var(Type); var(Subtype) ), 333 | !, 334 | fail. 335 | has_subtype(Type, Subtype) :- 336 | type_subtype(Type, Subtype), 337 | !. 338 | has_subtype(Type, Subtype) :- 339 | error:must_be(nonvar, Type), 340 | error:must_be(arbitrary_type, Subtype), 341 | \+ counter_example(Type, Subtype, _), 342 | assert(type_subtype(Type, Subtype)). 343 | 344 | % find a value (Example) which belongs to Subtype but not 345 | % to Type. This demonstrates that Subtype is not a strict 346 | % subset of Type. 347 | counter_example(Type, Subtype, Example) :- 348 | between(1,100,_), 349 | quickcheck:arbitrary(Subtype, Example), 350 | \+ error:is_of_type(Type, Example), 351 | !. 352 | 353 | 354 | %% type_intersection(?Type, ?IntersectionType) 355 | % 356 | % Multifile predicate for declaring that Type has an IntersectionType. 357 | % See type_subtype/2 for further details. 358 | :- dynamic type_intersection/2. 359 | :- multifile type_intersection/2. 360 | 361 | 362 | %% has_intersection(Type, IntersectionType) is semidet 363 | % 364 | % True if some value of IntersectionType is also of Type. See 365 | % has_subtype/2 for further details. 366 | has_intersection(Type, Intersection) :- 367 | ( var(Type); var(Intersection) ), 368 | !, 369 | fail. 370 | has_intersection(Type, Intersection) :- 371 | type_intersection(Type, Intersection), 372 | !. 373 | has_intersection(Type, Subtype) :- 374 | error:must_be(nonvar, Type), 375 | error:must_be(arbitrary_type, Subtype), 376 | shared_value(Type, Subtype, _), 377 | assert(type_intersection(Type, Subtype)). 378 | 379 | % Find a value shared by both Type and Subtype 380 | shared_value(Type, Subtype, Value) :- 381 | between(1,100,_), 382 | quickcheck:arbitrary(Subtype, Value), 383 | error:is_of_type(Type, Value), 384 | !. 385 | 386 | 387 | %% known_type(?Type:type) is semidet. 388 | % 389 | % True if Type is a type known to error:has_type/2. Iterates 390 | % all known types on backtracking. Be aware that some types are 391 | % polymorphic (like `list(T)`) so Type may be a non-ground term. 392 | % 393 | % As a convenience, the type named `type` describes the set of all 394 | % values for which `known_type/1` is true. 395 | known_type(Type) :- 396 | dif(Type, impossible), % library(error) implementation detail 397 | clause(error:has_type(Type, _), _Body, _Ref). 398 | 399 | 400 | :- multifile error:has_type/2. 401 | error:has_type(type, T) :- 402 | known_type(T). 403 | -------------------------------------------------------------------------------- /prolog/readme.txt: -------------------------------------------------------------------------------- 1 | ../README.md -------------------------------------------------------------------------------- /t/determinism.pl: -------------------------------------------------------------------------------- 1 | :- use_module(library(mavis)). 2 | :- use_module(library(tap)). 3 | 4 | %! even(+X:integer) is semidet. 5 | even(X) :- 6 | 0 is X mod 2. 7 | 8 | %! is_graph(+Graph) is semidet. 9 | % 10 | % True if Graph is a well formed graph 11 | is_graph(graph(Instance,Inference,Schema)) :- 12 | atom(Instance), 13 | atom(Inference), 14 | atom(Schema). 15 | 16 | error:has_type(graph, X) :- 17 | is_graph(X). 18 | 19 | :- multifile quickcheck:arbitrary/2. 20 | quickcheck:arbitrary(graph, graph(A,B,C)) :- 21 | arbitrary(atom, A), 22 | arbitrary(atom, B), 23 | arbitrary(atom, C). 24 | 25 | %! graph_instance(+Graph:graph, ?GraphName:atom) is det. 26 | graph_instance(graph(Instance,_,_),Instance). 27 | 28 | frobnify(A,B) :- 29 | the(integer,A), A=B. 30 | 31 | brofnify(A,B) :- 32 | the(string,A),A=B. 33 | 34 | %! first_string(+X:list(string), ?Y:string) is det. 35 | first_string([X|_],X). 36 | 37 | %! back_and_forth(+X,-Y) is det. 38 | % back_and_forth(-X,+Y) is semidet. 39 | back_and_forth(X,Y) :- 40 | Y=[1|X]. 41 | 42 | %! something(+X:integer,-Y:integer) is det. 43 | something(X,Y) :- 44 | ( even(X) 45 | -> Y is X * 2 46 | ; Y is X * 3 47 | ). 48 | 49 | %! dependent_type(+X:integer,+Y:([A]>>(A 14 | "hello ", 15 | string(Name). 16 | 17 | %% from_name(Codes, Atom, Extra:atom) 18 | from_name(Codes, Atom, Extra) :- 19 | Extra = extra, 20 | atom_codes(Atom, Codes). 21 | 22 | %% lazy(Foo) 23 | lazy(_). 24 | 25 | /** 26 | * elt(+X,List) is nondet. 27 | * elt(-X,+List) is nondet. 28 | * 29 | * Two modelines with no typing information 30 | */ 31 | elt(X,L) :- 32 | member(X,L). 33 | 34 | /** 35 | * elt_det(+X:integer,+List:list(integer)) is det. 36 | * 37 | * Two modelines with no typing information 38 | */ 39 | elt_det(X,L) :- 40 | ( member(X,L) 41 | -> true 42 | ; false). 43 | 44 | --------------------------------------------------------------------------------