This is a stoics.infrastructure pack for handling option arguments. The main concept is to treat options as naive Prolog lists which the programmer can manipulate and specialise if they need to, while providing a small number of predicates that manage basic common operations on options. Options are particularly important in the context of SWI packs, as making code publicly available to others often involves allowing for variations in the behaviour of the code.
The library provides simple extensions to the basic list manipulation predicates. In many cases it is just the error handling that is the main difference to standard predicates.
Technically the library is designed on the semantics of memberchk/2. Looking for an Option in a list of options, memberchk/2 will return the leftmost match. Library(options) sees options as a concatenation (append/3) of the user provided options (arguments for hereon) and the defaults provided by the predicate.
The default option values for a predicate are given by a predicate of the same name but postfixed by '_defaults'. The library also allows for reading user specific default options by reading profiles from a file located at $HOME/.pl/<pred_name>.pl, if that file exists. Each options file should have a number of option terms given as facts.
Some distinctive features of pack(options)
debug(Dbg) terms which optionise calls to debug/1
For an example see program options_example_sort_defaults.pl in examples directory.
?- edit( pack(options/examples/ex_sort) ). ?- [pack(options/examples/ex_sort)]. ?- ex_sort( [a,b,e,c,b], Ord, true ). Ord = [a, b, c, e]. ?- ex_sort( [a,b,e,c,b], Ord, debug(true) ). % Input list length: 5 % Output list length: 4 Ord = [a, b, c, e]. ?- ex_sort( [a,b,e,c,b], Ord, order(>) ). Ord = [e, c, b, a]. ?- ex_sort( [a,b,e,c,b], Ord, duplicates(true) ). Ord = [a, b, b, c, e].
Create file $HOME/.pl/ex_sort.pl with content
order(>).
?- ex_sort( [a,b,e,c,b], Ord, true ). Ord = [e, c, b, a].
Default for user is now order(>) which can still be over-ridden at invocation
?- ex_sort( [a,b,e,c,b], Ord, order(<) ). Ord = [a, b, c, e].
Predicates
Thanks to Jan Wielemaker for fixing an issue with expanding the $HOME variable and missing curly brackets in the errors DCG (2016/11/14).
debug(options_append).
The predicate can process debug(Dbg) a commonly used option. Default should be provided by PredName caller.
The infrastructure allows for other options to be added easily.
OAopts term or list of
scale(Scale=false)
or true (full scale, subtract mean and divide by stadard deviation) or centre (subtract mean)
arity(Arity= -1)
the arity of the caller, only used for reporting type errors for now
atoms(-Atoms)
removes atoms from input arguments, and instantiates them into Atoms. OptS == true, is an exception: Atoms is instantiated to []
check_types(ChkTypes=true)
if the defaults predicate returns a default ofoptions_types(OTypes), this is removed and used to check the types of the supplied options. OTypes should be OptName-Type pairs list with Type being one of those recognised by type/2 inpack(pack_errors).
extra_arg(Arg)
multiple allowed. All Arg(s) so passed are added to the Args passed to the defaults predicate, but not to the generated options. Allows for instance to pass arguments of the call itself to the defaults predicate without those arguments being added to the Options list
foreign(-Foreign)
instantiates to all input options that do not have matching default term structure
debug(Dbg=none)
if true debug this call, and call prolog_debug:debug_topic(Pname).
if false trun debugging off for this call.
Else Dbg can be a debug term (other than none,false,true) or list of debug terms.
funnel(Proccess)
as process() below, but leaves processed
options in All.
pack(Pack)
caller pack, only used to report type errors for nowprocess(Proccess)
with Proccess in
will turn on debugging according to debug/0,1,2 options, see below
remove_types(Rtypes=true)
to pass options_types(OTypes) to the result Options use Rtypes == falseWhen processing debugging options in All, the first matching term of the following is used:
short
for debug(true)
debug(Dbgs)
short
for debug(Dbgs,_Prior)
debug(Dbgs,Prior)
Prior is the prior status
of debug(PredName). For each element of Dbgs call RHS:
debug(PredName)
same as
nodebug(PredName)
same as
true same as
debug(_)
same as
debug(Other)
other
?- assert( demo_defaults(ls(true)) ). ?- options_append( demo, ls(false), All ). All = [ls(false), ls(true)]. ?- options_append( demo, debug, All, process(debug) ). All = [ls(true)]. ?- options_append( demo, [debug(true),ls(false)], All, [process(debug),debug(true)] ). Turning debugging on for predicate handle: demo All = [ls(false), ls(true)]. % Note that the debug(options_append) has been removed. ?- options_append( demo, debug, All, process(debug) ). All = [ls(true)]. ?- [pack(options/examples/ex_app)]. ?- ex_app. atoms([a,b,c]) opts([frg1(false),opt1(false),opt1(true)]) foreign([frg1(false)]) true.
The default OAopts list is [funnel(debug)].
debug(_,Format,Args) iff debug(true) is the first debug(_) term in
list Opts
?- options_debug( 'A simple message at: ~w', noon, [debug(true)] ). ?- options_debug( 'A simple message at: ~w', noon, [] ).
The predicate does not check arities.
The order in OptsOut follows the order in Onames.
PropOpts control the predicate behaviour
match(all) for no removalThis predicate is often called at the end of a deterministic call that depends on a set of options.
Currently the only option that is restored is
debug(Dbg)Internals; The predicate looks for any macthing '$restore'(Self,OptName,Status), so it should be extensible to other state-based options processing.
memberchk( Term, OptS )
succeeds of single Term in the possibly listed term list TermS,
then any unbound parts of TermS maybe become more ground.
This predicate can be used to instantiate return options.
OptS and TermS are passed through en_list/2.
?- options_return( cnm(Cnm), [abc(x),cnm(symbols)] ). Cnm = symbols. ?- options_return( [data(Dt),cnm(Cnm)], [abc(x),cnm(symbols)] ). Cnm = symbols
options(Opt,Opts)= succeeds.
Opts can in addition to Opt include
call_module(Mod=user)
which defines the calling module if one is not in Goal
?- options_call( write(true), (write(true),nl), write(true) ). true true. ?- options_call( write(flase), (write(true),nl), write(false) ). true. ?- options_call( write(true), user:(write(true),nl), write(true) ). true true.
Opts
call_module(Mod=user)
the module in which to call extended Goal
?- options_call( plus(2,X), plus(1) ). X = 3
options(debug(true),Opts), with Restore
being instantiated to a term that can be used to restore the
original debug state of Topic (see options_restore/2).
?- options_debug_topic( ex1, [debug(false)], Restore ). Restore = []. ?- options_debug_topic( ex1, [debug(true)], Restore ). Restore = ['$restore'(ex1, debug, false)].
Currently:
?- options_version( Vers, Date ). Date = date(2017,3,10), Vers = 0:5:0.
Opts can also be non list as it is passed through en_list/2.
Options
The predicate fails silently if the first Required option with equivalent "shape" in Opts fails to pattern match (unlike classic memberchk/2).
?- options( x(y), [x(x)] ). false. ?- options( x(y), [x(x),x(y)] ). false. ?- options( x(X), [a(b),c(d),x(y),x(x)] ). X=y. ?- options( [a(X),c(b)], [a(b),x(x),b(c)] ). ERROR: Required option: c(b), not present in options: [a(b),x(x)] % Execution Aborted ?- options( x(X), [a(b),c(d),x(y),x(x)], rem_opts(Rem) ). X = y, Rem = [a(b), c(d)]. ?- options( x(X), [a(b),c(d),x(y),x(x)], en_list(true) ). X= [y]. ?- options( a(A), [a(X),b(c)], ground(error) ). ERROR: pack(options): Option should be ground, but found: a(_G1470), in options: [a(_G1470),b(c)] ?- options( a(A), [a(X),b(c)], ground(true) ). false. ?- options( a(A), [a(X),b(c)] ). A = X. ?- options( a(A), [a(X),b(c)], ground(false) ). A = X. ?- options( a(b), [a(a),a(b),b(c)], true(T) ). T = fail. ?- options( a(A), [a(a),a(b),b(c)], true(T) ). A = a, T = true. ?- options( a(a), [a(a),a(b),b(c)], true(T) ). T = true.