consult/[1,2]

Module: builtins

consult/1 — load a Prolog file
consult/2 — load a Prolog file, with options
consultq/1 — load a Prolog file, without messages
reconsult/1 — load a Prolog file, updating the prolog database

FORMS

consult(FileSpec)

consult(FileSpec, Options)

[File | Files ]
         Synonym for consult(FileSpec) when FileSpec is [File | Files ]

consultq(File)

reconsult(File)

[-File | Files ]
         Equivalent to a sequence of reconsult/consult calls, corresponding to the appearance of - or no -.

DESCRIPTION

FileSpec should be instantiated either to an atom that is the name of a file, or to a list of atoms which are names of files. For each File occurring on FileSpec,

  1. File is opened and read,
  2. Any clauses currently in memory which were read and asserted previously from this same File are erased,
  3. The clauses occurring in File are asserted into the database,
  4. Any directives occurring in File are executed immediately when encountered.

consultq/1 behaves exactly like consult/1, except that printing of normal consult/1 messages on the terminal is suppressed. [Note, however, that if the File does not exist, an error message will still be printed.]

reconsult/1 is identical to consult/1 and is preserved for historical consistency.

consult/1, reconsult/1, and consultq/1 are defined by :

consult(File) :- consult(File, [ ]) .

reconsult(File :- consult(File, [ ]) .

consultq(File) :- consult(File, [verbosity(quiet) ]) .

If File is the atom user, then clauses and commands will be read in from the keyboard until an end of file is read.

The Options argument of consult/2 is a list of consult options, and their effects, are as follows :

verbosity(Value)
      Value = noisy/quiet; turns on/off the printing of messages during consulting.

tgtmod(TgtMod)
      Any clauses in File which are not explicitly enclosed in module begin/end directives will be asserted to module TgtMod. The default value of TgtMod is user.

search_path(DirPathList)
      DirPathList is a list of directory path names. The File(s) to be consulted are searched for on this path. If the current directory is not listed on DirPathList, it is added at the beginning.

strict_search_path(DirPathList)
      Like search_path(DirPathList), but the current directory is not added even if not present on DirPathList.

consult(Value)
      Value = true/false. If Value = true, previous clauses from the File being consulted are not erased, so that the net effect is additive.

ensure_loaded(Value)
      Value = true/false. This option has effect only when operating under one of the ALS development shells(ALS IDE or the TTY shell). If Value = true, and if File has previously been consulted, no action is taken for File. If Value = false, File is consulted.

EXAMPLES

Let the file fruit.pro contain:

fruit(apple).
fruit(X) :- nut(X).
fruit(orange).
nut(hazelnut).

Then:

?- consult(fruit).

yes.
?- listing.

% user:fruit/1
fruit(apple).
fruit(_A) :- nut(_A).
fruit(orange).

% user:nut/1
nut(hazelnut).

yes.

Now, using a separate editor process, edit fruit.pro so that it contains:

fruit(apple).
fruit(X) :- nut(X).
fruit(raspberry).
nut(hazelnut).
nut(acorn).

Now, consult fruit.pro again:

?- consult(fruit).

yes.
?- listing.

% user:fruit/1
fruit(apple).
fruit(_A) :- nut(_A).
fruit(raspberry).

% user:nut/1
nut(hazelnut).
nut(acorn).

yes.

The following example illustrates the practice of putting calls to consult/1 inside of files to be(re) consulted. We have the three files with contents as follows :

letters.pro
-----------
symbol(a).
symbol(b).
symbol(c).

numbers.pro
-----------
symbol('1').
symbol('2').
symbol('3').

topfile.pro
-----------
symbol(x).
symbol(y).
symbol(z).

:- consult(letters).
:- consult(numbers).

The following conversation illustrates the effect of repetitive consult (or reconsult) with embedded consults:

?- consult(letters).

yes.

?- listing.
%user:symbol/1
symbol(a).
symbol(b).
symbol(c).
yes.

?- consult(topfile).

yes.

?- listing.
%user:symbol/1
symbol(a).
symbol(b).
symbol(c).
symbol(x).
symbol(y).
symbol(z).
symbol('1').
symbol('2').
symbol('3').

NOTES

reconsult/1 is not compatible with the DEC-10 notion of reconsult. DEC-10 reconsult would, upon seeing a procedure not already seen in a file, wipe out or abolish all clauses for that predicate before adding the new clause in question.

The present semantics of reconsult/1 are that all clauses which were previously defined in a File being loaded are wiped out, with new clauses replacing (positionally in the procedure) any old clauses. Thus, a procedure that is defined by several files will not be entirely wiped out when reconsult/1 is invoked on just one of the procedure’s files – only those clauses defined by the one given File are wiped out and subsequently replaced.

The file user is special. When user is consulted or reconsulted, the input clauses will be taken from the user’s terminal. The end-of-file character (often Control-D or Contol-Z) should be used to terminate the consultation and return to the shell.

SEE ALSO