This library realises emulation of IF/Prolog. As with all the emulation layers in the dialect directory, the emulation has been established on `as needed' basis from porting programs. This implies that the emulation is incomplete. Emumated directives, predicates and libraries are often not 100% compatible with the IF/Prolog version.

Note that this emulation layer targets primarily IF/Prolog version 5.

Please help extending this library and submit patches to bugs@swi-prolog.org.

 ifprolog_goal_expansion(+In, +Out)[multifile]

goal_expansion rules to emulate IF/Prolog behaviour in SWI-Prolog. The expansions below maintain optimization from compilation. Defining them as predicates would loose compilation.

 context(:Goal, Handler)

Is mapped to catch(Goal, Error, Recover) is Handler is error(_,_) => Recover. Other cases are not covered by the emulation.

 asserta(Head, Body) is det[private]

 assertz(Head, Body) is det[private]

 retract(Head, Body) is det[private]

Mapped to asserta((Head:-Body)), etc. Note that this masks SWI-Prolog's asserta/2, etc.

 ifprolog_term_expansion(+In, +Out)[multifile]

term_expansion rules to emulate IF/Prolog behaviour in SWI-Prolog.

 meta(+ListOfPI)[private]

Mapped to module_transparent/1. Not sure whether this is correct. It surely is not very elegant to map to a deprecated feature. Luckily, although the module_transparent/1 API is deprecated, the underlying functionality is still core of the module system.

Note that if :- meta appears inside a module interface, the predicate is also exported.

 export(+ListOfPI) is det[private]

 discontiguous +ListOfPI is det[private]

Mapped to comma-lists

 module(+Name)[private]

 begin_module(+Name)[private]

 end_module(+Name)[private]

These are emulated correctly, provided module/1 is the first term of the file and the implementation is part of the same file. Begin/end are ignored.

 pi_list_to_pi_term(+List, -CommaList) is det[private]

 push_ifprolog_library[private]

Pushes searching for dialect/ifprolog in front of every library directory that contains such as sub-directory.

 push_ifprolog_file_extension[private]

Looks for .pro files before looking for .pl files if the current dialect is pro. If the dialect is not active, the .pro files are found as last resort.

 calling_context(-Context)

Mapped to context_module/1.

 context(:Goal, +Mapping)

IF/Prolog context/2 construct. This is the true predicate. This is normally mapped by goal-expansion.

bug

- Does not deal with IF/Prolog signal mapping

 block(:Goal, +Tag, :Recovery)

 exit_block(+Tag)

 cut_block(+Tag) is semidet

The control construct block/3 runs Goal in a block labelled Tag. If Goal calls exit_block/1 using a matching Tag, the execution of Goal is abandoned using exception handling and execution continues by running Recovery. Goal can call cut_block/1. If there is a block with matching Tag, all choice points created since the block was started are destroyed.

bug

- The block control structure is implemented on top of catch/3 and throw/1. If catch/3 is used inside Goal, the user must ensure that either (1) the protected goal does not call exit_block/1 or cut_block/1 or (2) the Catcher of the catch/3 call does not unify with a term block(_,_).

 modify_mode(+PI, -OldMode, +NewMode) is det

Switch between static and dynamic code. Fully supported, but notably changing static to dynamic code is not allowed if the predicate has clauses.

 debug_mode(:PI, -Old, +New)

Old is not unified. Only New == off is mapped to disable debugging of a predicate.

 ifprolog_debug(:Goal)

Map IF/Prolog debug(Goal)@Module. This should run Goal in debug mode. We rarely needs this type of measures in SWI-Prolog.

 debug_config(+Key, -Current, +Value)

Ignored. Prints a message.

 float_format(-Old, +New)

Ignored. Prints a message. Cannot be emulated. Printing floats with a specified precision can only be done using format/2.

 program_parameters(-List:atom)

All command-line argument, including the executable,

 user_parameters(-List:atom)

Parameters after --.

 match(+Mask, +Atom) is semidet

Same as once(match(Mask, Atom, _Replacements)).

 match(+Mask, +Atom, ?Replacements) is nondet

Pattern matching. This emulation should be complete. Can be optimized using caching of the pattern-analysis or doing the analysis at compile-time.

 lower_upper(+Lower, -Upper) is det

lower_upper(-Lower, +Upper) is det

Multi-moded combination of upcase_atom/2 and downcase_atom/2.

 load(File)

Mapped to consult. I think that the compatible version should only load .qlf (compiled) code.

 unload(+Module) is det[private]

Unload the named module.

bug

- : What to do with modules that are not associated to a file?

 file_test(+File, +Mode)

Mapped to access_file/2 (which understand more modes). Note that this predicate is defined in the module system to allow for direct calling.

 filepos(@Stream, -Line)

from the IF/Prolog documentation The predicate filepos/2 determines the current line position of the specified input stream and unifies the result with Line. The current line position is the number of line processed + 1

 getcwd(-Dir)

The predicate getcwd/1 unifies Dir with the full pathname of the current working directory.

 filepos(@Stream, -Line, -Column)

from the IF/Prolog documentation The predicate filepos/2 determines the current line position of the specified input stream and unifies the result with Line. The current line position is the number of line processed + 1

 assign_alias(+Alias, @Stream) is det

 writeq_atom(+Term, -Atom)

Use writeq/1 to write Term to Atom.

 write_atom(+Term, -Atom)

Use write/1 to write Term to Atom.

 current_error(-Stream)

Doesn't exist in SWI-Prolog, but user_error is always an alias to the current error stream.

 write_formatted_atom(-Atom, +Format, +ArgList) is det

 write_formatted(+Format, +ArgList) is det

 write_formatted(@Stream, +Format, +ArgList) is det

Emulation of IF/Prolog formatted write. The emulation is very incomplete. Notable asks for dealing with aligned fields, etc.

bug

- Not all format characters are processed

- Incomplete processing of modifiers, fieldwidth and precision

To be done

- This should become goal-expansion based to process format specifiers at compile-time.

 format_modifiers(-Flags, -FieldLength, -Precision) is det[private]

Read the IF/Prolog format modifiers. We currently do not process any of the modifiers! Some code seems to be using e.g. %07lx. We assume this is the same as -07x (assuming l=left).

 get_until(+SearchChar, -Text, -EndChar) is det

 get_until(@Stream, +SearchChar, -Text, -EndChar) is det

Read input from Stream until SearchChar. Unify EndChar with either SearchChar or the atom end_of_file.

 atom_part(+Atom, +Pos, +Len, -Sub) is det

True when Sub is part of the atom [Pos,Pos+Len). Unifies Sub with '' if Pos or Len is out of range!?

 atom_prefix(+Atom, +Len, -Sub) is det

Unifies Sub with the atom formed by the first Len characters in atom.

• If Len < 1, Sub is unified with the null atom ''.
• If Len > length of Atom, Sub is unified with Atom.

 atom_suffix(+Atom, +Len, -Sub) is det

Unifies Sub with the atom formed by the last Len characters in atom.

• If Len < 1, Sub is unified with the null atom ''.
• If Len > length of Atom, Sub is unified with Atom.

 atom_split(+Atom, +Delimiter, ?Subatoms)

Split Atom over Delimiter and unify the parts with Subatoms.

 if_concat_atom(+List, +Delimiter, -Atom) is det

True when Atom is the concatenation of the lexical form of all elements from List, using Delimiter to delimit the elements.

The behavior of this ifprolog predicate is different w.r.t. SWI-Prolog in two respect: it supports arbitrary terms in List rather than only atomic and it does not work in mode -,+,+.

 if_concat_atom(+List, -Atom) is det

True when Atom is the concatenation of the lexical form of all elements from List. Same as if_concat_atom/3 using '' as delimiter.

 getchar(+Atom, +Pos, -Char)

Unifies Char with the Position-th character in Atom If Pos < 1 or Pos > length of Atom, then fail.

 parse_atom(+Atom, +StartPos, ?EndPos, ?Term, ?VarList, ?Error)

Read from an atom.

Arguments:

StartPos	- is 1-based position to start reading
Error	- is the 1-based position of a syntax error or 0 if there is no error.

 index(+Atom, +String, -Position) is semidet

True when Position is the first occurrence of String in Atom. Position is 1-based.

 list_length(+List, ?Length) is det

Deterministic version of length/2. Current implementation simply calls length/2.

 for(+Start, ?Count, +End) is nondet

Similar to between/3, but can count down if Start > End.

 prolog_version(-Version)

Return IF/Prolog simulated version string

 proroot(-Path)

True when Path is the installation location of the Prolog system.

 system_name(-SystemName)

True when SystemName identifies the operating system. Note that this returns the SWI-Prolog arch flag, and not the IF/Prolog identifiers.

 localtime(+Time, ?Year, ?Month, ?Day, ?DoW, ?DoY, ?Hour, ?Min, ?Sec)

Break system time into its components. Deefines components:

Year	Year number	4 digits
Month	Month number	1..12
Day	Day of month	1..31
DoW	Day of week	1..7 (Mon-Sun)
DoY	Day in year	1..366
Hour	Hours	0..23
Min	Minutes	0..59
Sec	Seconds	0..59

Note that in IF/Prolog V4, Year is 0..99, while it is a four-digit number in IF/Prolog V5. We emulate IF/Prolog V5.

 current_global(+Name) is semidet

 get_global(+Name, ?Value) is det

 set_global(+Name, ?Value) is det

 unset_global(+Name) is det

IF/Prolog global variables, mapped to SWI-Prolog's nb_* predicates.

 current_default_module(-Module) is det

Name of the toplevel typein module.

 set_default_module(+Module) is det

Set the default toplevel module.

 asserta_with_names(@Clause, +VarNames) is det

 assertz_with_names(@Clause, +VarNames) is det

 clause_with_names(?Head, ?Body, -VarNames) is det

 retract_with_names(?Clause, -VarNames) is det

Predicates that manage the database while keeping track of variable names.

 predicate_type(:PI, -Type) is det

True when Type describes the type of PI. Note that the value linear seems to mean you can use clause/2 on it, which is true for any SWI-Prolog predicate that is defined. Therefore, we use it for any predicate that is defined.

 current_visible(@Module, @PredicateIndicator)

FIXME check with documentation

 current_signal(?Signal, ?Mode) is nondet

True when Mode is the current mode for handling Signal. Modes are on, off, default, ignore. Signals are abort, alarm, interrupt, pipe, quit, termination, user_1 and user_2.

To be done

- Implement

 digit(+A)

Is the character A a digit [0-9]

 letter(+A)

Is the character A a letter [A-Za-z]