prolog - Remove item from multiple lists -


i have subproblem solution way larger suspect necessary.

the problem defined follows

remove x groups group has id between y , z or , b

expressed pseudo query looks y,z,a,b set 0,1,3,4

remove(x,         [ period(0,1), period(3,4) ],        [            group(0, [ subgroup([_,_,x,_,_]), subgroup([x])]),           group(1, [ subgroup([x])]),           group(2, [ subgroup([_,_,x])]),           group(3, [ subgroup([_,x,_])]),           group(4, [ subgroup([x,_,_])])        ], updatedgroups).

the result be

updatedgroups = [      group(0, [ subgroup([_,_,_,_]), subgroup([])]),     group(1, [ subgroup([])]),     group(2, [ subgroup([_,_,x])]),     group(3, [ subgroup([_,_])]),     group(4, [ subgroup([_,_])]) ]

so, solution is:

while start of current period less or equal end of current period, removal of x in groups, while "incrementing" start of day. repeat until no more periods

the removal of x in groups done "looping" groups , check if matches period, , if remove user subgroups, again done "looping".

this tedious straight forward solution, problem quite find myself doing stuff this, , cannot find approaches in less comprehensive way.

are there other approaches mine not cover 50+ lines?

updated

thanks lot, code became cleaner - might go further, possible post here (this modified bit - logic there)

inperiods(day, [ period(start,end) | _ ]) :- between(start,end, day). inperiods(day, [ _ | remainingperiods ]) :- inperiods(day, remainingperiods).  rulegroupsinperiod(periods, rulegroup(day,_)) :- inperiods(day, periods).  removeuserfromrelevantrulegroups(userid, periods, rulegroups, updatedrulegroups) :-     include(rulegroupsinperiod(periods), rulegroups, includedrulegroups).     exclude(rulegroupsinperiod(periods), rulegroups, excludedrulegroups),     maplist(updaterulegroup(userid), includedrulegroups, updatedincludedrulegroups)     append(updatedincludedrulegroups, excludedrulegroups, updatedrulegroups).  updaterulegroup(userid, rulegroup(x, rulelist), rulegroup(x, updatedrulelist)) :-     maplist(updaterule(userid), rulelist, updatedrulelist).  updaterule(userid, rule(x, userlist), rule(x, updateduserlist)) :-     delete(userlist, userid, updateduserlist).

yes.

the pattern describe common, , serious prolog systems ship powerful meta-predicates (i.e., predicates arguments denote predicates) let describe , many other common situations in flexible manner, using @ few simple additional definitions concrete relations.

richard o'keefe's proposal an elementary prolog library contains descriptions , implementations of many such predicates, becoming increasingly available in major prolog implementations , in prologue prolog.

in particular, should study:

  • include/3
  • exclude/3
  • maplist/[2,3]

note though many of described predicates impure in sense destroy declarative properties of code. in contrast true relations, won't able use them in all directions while preserving logical soundness.

exercise: of 3 predicates mentioned above, if any, preserve when else pure, , which, if any, not?


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