Release 3 had the notion of multiple language modes: iso and
sicstus. Release 4 does not have this notion. The syntax and
semantics of the Prolog language correspond to the previous
iso language mode.
The exact rules for translating DCG rules to plain Prolog clauses have not been laid down in a standard, but there is a broad consensus in the Prolog community about what they should mean. One of the guiding principles is that the translation should be steadfast, in particular that the translated code should always treat its last argument as an output argument and not use it “too early”. In some cases, a non-steadfast translation was produced in release 3. This has been corrected in release 4.
In release 3, terms containing attributed variables and blocked goals
could be asserted, copied, gathered as solutions to findall/3
and friends, and raised as exceptions. The copy would contain new
attributed variables with the attributes copied. This operation could
be very expensive, could yield unexpected results and was not always
safe e.g. in the context of CLPFD constraints. In release 4, the
semantics of this operation has changed: in the copy, an attributed
variable is simply replaced by a plain, brand new variable. Of
course, if the same attributed variable occurs more than once, the
same plain variable will occur in the corresponding places in the
copy. If the attributes are relevant, then the program can obtain them by
using the new built-in predicate copy_term/3 described below.
The infix operator ‘#’ (bitwise exclusive or) has been renamed to ‘\’.
Atoms can now contain the NUL character, i.e. character code
zero. It is classified as whitespace and must therefore be entered
using escapes. As an example 'a\0\a' is a three character atom
containing two as separated by a NUL.
Internally, atom names and other encoded strings, use the non-shortest form ‘0xC0 0x80’ to encode NUL. This is similar to how NUL is handled by Tcl/Tk and Java.
The language and wcx Prolog flag have been dropped.
The profiledcode value of the compiling Prolog flag has been dropped.
Several new Prolog flags have been added.
See Prolog Flags in the SICStus Prolog Manual.
The wcx property has been dropped.
Several new stream properties have been added.
See stream_property/2 in the SICStus Prolog Manual.
Several new statistics keywords have been added.
See statistics/[0,1] in the SICStus Prolog Manual.
The set of built-in predicates has changed slightly. The following predicates have been removed:
'C'/3This was used in the Prolog translation of DCG rules. It could trivially be replaced by unifications and served no other reasonable purpose.
get0/[1,2]put/[1,2]These used to have an overloaded semantics meaning one thing on binary streams and another thing on text streams. They have been subsumed by their ISO counterparts.
get/[1,2]tab/[1,2]skip/[1,2]Although these do not have ISO counterparts, they have been removed
for being in the spirit of get0/[1,2] and put/[1,2].
We have provided skip_char/[1,2], skip_code/[1,2], and
skip_byte/[1,2] as an ISO style replacement for
skip/[1,2].
ttyget0/1ttyget/1ttynl/0ttyput/1ttyskip/1ttytab/1ttyflush/0These used to exist as shorthands for the respective predicate with an
additional user argument. In most cases, the “respective
predicate” is one of the non-ISO style predicate mentioned above, so
there was no point in keeping the shorthand.
fileerrors/0nofileerrors/0These used to exist as shorthands for set_prolog_flag/2 with
specific arguments, and so can be trivially replaced.
call_residue/2Dropped because it was not possible to ensure the correct behavior in
all circumstances, it relied heavily on copying terms with attributed
variables, and it was not needed by any library module. It has been
replaced by a similar predicate, call_residue_vars/2, which should
suffice in most cases where call_residue/2 was used; see below.
undo/1Dropped because it was not possible to ensure the correct behavior in
all circumstances. Users that know what they are doing can still call
the unsupported predicate prolog:undo/1. The argument should
have a module prefix.
help/0version/0version/1These predicates, managing and displaying messages, can be easily emulated by feaures of the message system.
fcompile/1load/1These predicates used to compile Prolog source code into ‘.ql’ files, and load such files. ‘.ql’ files serve a purpose when boot-strapping the Prolog system, but offer no advantages over ‘.po’ files, the Prolog object code format used by other built-in predicates.
load_foreign_files/2This predicate provided a shorthand for building and loading a temporary foreign resource. Working with foreign resources is straightforward, and so the shorthand was dropped.
require/1This predicate provided a shorthand for locating and loading library
predicates. This was originally introduced for a compatibility reason
that is now obsolete. It is straightforward to provide the necessary
:- use_module/2 directives, and so the shorthand was dropped.
profile_data/4profile_reset/1As of release 4.2, the execution profiling technology has been reengineered, eliminating the need to specially instrument code before it could be profiled. The new scheme also keeps track of the number of calls per caller-callee pair. Execution profiling is available for compiled as well as interpreted code. These two predicates have been replaced by a small number of new ones.
The following predicates have been added:
call/NGeneralizes call/1. For example, call(p(1,2), a, b) is
equivalent to call(p(1,2, a, b)).
skip_char/[1,2]skip_code/[1,2]skip_byte/[1,2]ISO style replacements for the non-ISO style skip/[1,2].
call_residue_vars/2Called as follows:
call_residue_vars(:Goal, -Vars)
Executes the procedure call Goal, unifying Vars with
the list of residual variables that have blocked goals or attributes
attached to them. Please note: behaves differently from
call_residue/2 of release 3.
copy_term/3Called as follows:
copy_term(+Term, -Copy, -Body)
Unifies Copy with a copy of Term in which all variables have
been replaced by brand new variables, and all mutables by brand new
mutables. If Term contains variables with goals blocked on them,
or variables with attributes that can be interpreted as a goal
(see library(atts) in the SICStus Prolog Manual), then Body is unified with the conjunction of
such goals. If no such goals are present, then Body is unified with
the atom true. The idea is that executing Body
will reinstate blocked goals and attributes on the variables in Copy
equivalent to those on the variables in Term.
profile_reset/0profile_data/1print_profile/[0,1]coverage_data/1print_coverage/[0,1]As of release 4.2, the execution profiling technology has been reengineered, eliminating the need to specially instrument code before it could be profiled. Execution profiling is available for compiled as well as interpreted code. It has been generalized to support coverage analysis for compiled as well as interpreted code. The new scheme also keeps track of the number of calls per caller-callee pair. These are the relevant new built-in predicates.
Some predicates have been changed slightly; in most cases, this affects predicates that take a list of options:
[F1,F2,…]This is now a short-hand for load_files([F1,F2,…]).
is_mutable/1The predicate is_mutable/1 has been renamed to
mutable/1, in analogy with integer/1, atom/1 etc.
module/1The predicate module/1 has been renamed to
set_module/1, to avoid possible confusion with the
module/2 declaration.
format/[2,3]For the predicate format/[2,3], the semantics of the ‘~@’
spec has changed slightly: the goal Arg is called as if by
\+ \+ Arg, i.e. any bindings made by the goal are lost.
close/2Takes new options:
direction/1Specifies which directions to close.
open/4The wcx/1 option has been dropped.
Takes several new options.
See open/4 in the SICStus Prolog Manual.
absolute_file_name/[2,3]The ignore_underscores/1 option has been dropped.
The file_type/1 option value ql has been dropped,
whereas the option value executable is new.
The access/1 option values execute,
executable and search are new.
The glob/1 option is new, allowing to match file names against a
pattern.
If available, then the load
context directory (prolog_load_context/2) will be used as default directory.
load_files/2The load_type/1 option value ql has been dropped.
encoding_signature/1, encoding/1, subsuming the wcx/1 option of
release 3, and eol/1, are new options, corresponding to the
respective stream properties.
write_term/3The quoted_charset/1 option is new, reflecting the value of the
Prolog flag with the same name.
halt/1The predicate halt/1 now raises an internal exception like
halt/0. This gives surrounding Prolog and C code an opportunity
to perform cleanup.
append/3member/2memberchk/2These are now built-in, they used to reside in library(lists).
The hook user:term_expansion/[2,4] is replaced by the hook:
user:term_expansion(Term1, Layout1, Tokens,
Term2, Layout2, [Token|Tokens]).
The purpose of the new argument Tokens is to support multiple, independent expansion rules. The purpose of the arguments Layout1 and Layout2 is to support source-linked debugging of term-expanded code. Each expansion rule should have its unique identifying token Token.
The hook user:goal_expansion/3 is replaced by the following per-module hook:
M:goal_expansion(Term1, Layout1,
Module, Term2, Layout2).
Typically, Module has imported the predicate Term1 from module M. The purpose of the arguments Layout1 and Layout2 is to support source-linked debugging of goal-expanded code.