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/usr/lib/swipl/library/prolog_wrap.pl
All Application Manual Name SummaryHelp

  • swipl
    • library
      • error.pl
      • debug.pl -- Print debug messages and test assertions
      • apply.pl -- Apply predicates on a list
      • lists.pl -- List Manipulation
      • broadcast.pl -- Event service
      • predicate_options.pl -- Access and analyse predicate options
      • shlib.pl -- Utility library for loading foreign objects (DLLs, shared objects)
      • option.pl
      • thread_pool.pl
      • gensym.pl
      • settings.pl
      • arithmetic.pl
      • main.pl -- Provide entry point for scripts
      • readutil.pl -- Read utilities
      • operators.pl -- Manage operators
      • pairs.pl -- Operations on key-value lists
      • prolog_source.pl -- Examine Prolog source-files
      • quasi_quotations.pl -- Define Quasi Quotation syntax
      • url.pl -- Analysing and constructing URL
      • www_browser.pl -- Open a URL in the users browser
      • prolog_colour.pl
      • record.pl -- Access compound arguments by name
      • prolog_xref.pl -- Prolog cross-referencer data collection
      • occurs.pl -- Finding and counting sub-terms
      • ordsets.pl -- Ordered set manipulation
      • assoc.pl -- Binary associations
      • ugraphs.pl -- Graph manipulation library
      • iostream.pl -- Utilities to deal with streams
      • atom.pl -- Operations on atoms
      • prolog_pack.pl -- A package manager for Prolog
      • solution_sequences.pl -- Modify solution sequences
      • git.pl -- Run GIT commands
      • ctypes.pl -- Character code classification
      • utf8.pl -- UTF-8 encoding/decoding on lists of character codes.
      • base64.pl -- Base64 encoding and decoding
      • persistency.pl -- Provide persistent dynamic predicates
      • pure_input.pl -- Pure Input from files and streams
      • nb_set.pl -- Non-backtrackable sets
      • aggregate.pl -- Aggregation operators on backtrackable predicates
      • csv.pl -- Process CSV (Comma-Separated Values) data
      • dialect.pl -- Support multiple Prolog dialects
      • apply_macros.pl -- Goal expansion rules to avoid meta-calling
      • yall.pl -- Lambda expressions
      • prolog_code.pl -- Utilities for reasoning about code
      • dif.pl -- The dif/2 constraint
      • thread.pl -- High level thread primitives
      • rbtrees.pl -- Red black trees
      • nb_rbtrees.pl -- Non-backtrackable operations on red black trees
      • random.pl -- Random numbers
      • sandbox.pl -- Sandboxed Prolog code
      • prolog_format.pl -- Analyse format specifications
      • pprint.pl -- Pretty Print Prolog terms
      • modules.pl -- Module utility predicates
      • lazy_lists.pl -- Lazy list handling
      • edinburgh.pl -- Some traditional Edinburgh predicates
      • prolog_clause.pl -- Get detailed source-information about a clause
      • prolog_breakpoints.pl -- Manage Prolog break-points
      • dicts.pl -- Dict utilities
      • check.pl -- Consistency checking
      • ansi_term.pl -- Print decorated text to ANSI consoles
      • backcomp.pl -- Backward compatibility
      • writef.pl -- Old-style formatted write
      • charsio.pl -- I/O on Lists of Character Codes
      • sort.pl
      • base32.pl -- Base32 encoding and decoding
      • tables.pl -- XSB interface to tables
      • statistics.pl -- Get information about resource usage
      • varnumbers.pl -- Utilities for numbered terms
      • prolog_jiti.pl -- Just In Time Indexing (JITI) utilities
      • intercept.pl -- Intercept and signal interface
      • terms.pl -- Term manipulation
      • quintus.pl -- Quintus compatibility
      • codesio.pl -- I/O on Lists of Character Codes
      • prolog_debug.pl -- User level debugging tools
      • listing.pl -- List programs and pretty print clauses
      • make.pl -- Reload modified source files
      • increval.pl -- Incremental dynamic predicate modification
      • strings.pl -- String utilities
      • date.pl -- Process dates and times
      • help.pl -- Text based manual
      • prolog_wrap.pl -- Wrapping predicates
        • wrap_predicate/4
        • unwrap_predicate/2
        • current_predicate_wrapper/4
      • rwlocks.pl -- Read/write locks
      • shell.pl -- Elementary shell commands
      • explain.pl -- Describe Prolog Terms
      • threadutil.pl -- Interactive thread utilities
      • prolog_versions.pl -- Demand specific (Prolog) versions
      • wfs.pl -- Well Founded Semantics interface
      • optparse.pl -- command line parsing
      • prolog_profile.pl -- Execution profiler
      • qsave.pl -- Save current program as a state or executable
      • zip.pl -- Access resource ZIP archives
      • heaps.pl -- heaps/priority queues
      • prolog_history.pl -- Per-directory persistent commandline history
      • when.pl -- Conditional coroutining
      • prolog_trace.pl -- Print access to predicates
      • edit.pl -- Editor interface
      • prolog_stack.pl -- Examine the Prolog stack
      • prolog_codewalk.pl -- Prolog code walker
      • prolog_metainference.pl -- Infer meta-predicate properties
      • prolog_coverage.pl -- Coverage analysis tool
      • macros.pl -- Macro expansion
      • exceptions.pl -- Exception classification
      • oset.pl -- Ordered set manipulation
      • hashtable.pl -- Hash tables
      • coinduction.pl -- Co-Logic Programming
      • system.pl -- System utilities
      • prolog_autoload.pl -- Autoload all dependencies
      • prolog_config.pl -- Provide configuration information
      • portray_text.pl -- Portray text
      • win_menu.pl -- Console window menu
      • tty.pl -- Terminal operations
      • fastrw.pl -- Fast reading and writing of terms
      • files.pl
 wrap_predicate(:Head, +Name, -Wrapped, +Body) is det
Wrap the predicate referenced by Head using Body. Subsequent calls to Head call the given Body term. Body may call the original definition through Wrapped. Wrapped is a term of the shape below, where Closure is an opaque blob.
call(Closure(A1, ...))

Name names the wrapper for inspection using predicate_property/2 or deletion using unwrap_predicate/2. If Head has a wrapper with Name the Body of the existing wrapper is updated without changing the order of the registered wrappers. The same predicate may be wrapped multiple times. Multiple wrappers are executed starting with the last registered (outermost).

The predicate referenced by Head does not need to be defined at the moment the wrapper is installed. If Head is undefined, the predicate is created instead of searched for using e.g., the auto loader.

Registered wrappers are not part of saved states (see qsave_program/2) and thus need to be re-registered, for example using initialization/1.

An example of using wrap_predicate/4 for computing GCD:

    :- wrap_predicate(gcd(A,B,Gcd), gcd_wrap, W, gcd_wrap(W, A, B, Gcd)).

    gcd(X, Y, Gcd), X < Y => gcd(X, Y-X, Gcd).
    gcd(X, Y, Gcd), X > Y => gcd(Y, X-Y, Gcd).
    gcd(X, _, Gcd) => Gcd = X.

    gcd_wrap(call(Closure), X, Y, Gcd) :-
        functor(Closure, ClosureBlob, 3),
        X_eval is X,
        Y_eval is Y,
        call(ClosureBlob, X_eval, Y_eval, Gcd).

or (less efficient):

    gcd_wrap(call(Closure), X, Y, Gcd) :-
        functor(Closure, ClosureBlob, 3),
        call(ClosureBlob, X_eval, Y_eval, G),
        Gcd is G.
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