SWI-Prolog (SWISH): No permission to modify static procedure `(=)/2' -

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• no permission modify static procedure 1 answer

during playing around different list predicates in swi-prolog (swish), trying check if atom a part of list list1 defined in program list1 = [a,b,c,d].

i formulated query member(a, list1)., expecting along lines of simple 'yes' (just shows in youtube video @ 59:25), instead got warning

singleton variables: [list1]

and error

no permission modify static procedure `(=)/2'

from understand looking online, warning not important here. not understand, however, why error message while a member of list1.

i tried in 2 different ways:

1) adding list1 = [a,b,c,d]. program , querying member(a,list1). (which resulted in error above);

2) passing list1 = [a,b,c,d] directly interpreter , using same query ( member(a,list1). ), resulted in endless amount of results a shifted positions in head of list, so:

list1 = [a|_1186] list1 = [_1062, a|_1070] list1 = [_1062, _1068, a|_1076] list1 = [_1062, _1068, _1074, a|_1082] list1 = [_1062, _1068, _1074, _1080, a|_1088] 

is specific prolog version using, or missing simple?

edit

i aware similar question posed here , did not manage understand answer (nor question) going things dynamic have not yet encountered in prolog. looking more general, more 'high-level' answer have found posing question.

i defined in program list1 = [a,b,c,d].

this not does. define predicate =/2:

2 ?- write_canonical( (list1 = [a,b,c,d]) ). =(_,[a,b,c,d])

^{(the ?-, or 2 ?- see there, interactive prompt of prolog system; swi prolog in case. whatever goes on line after have typed; , on next line see system's response).}

of course tramples on existing built-in definition = unification predicate. , hence error says precisely that. , yes, is important.

to "define" list in prolog, can define predicate

8 ?- [user]. p([1,2,3,4]). 

such can query

9 ?- p(list1). list1 = [1, 2, 3, 4]. 

and work further list1,

10 ?- p(list1), member(a,list1). list1 = [1, 2, 3, 4], = 1 ; list1 = [1, 2, 3, 4], = 2 ; list1 = [1, 2, 3, 4], = 3 ; list1 = [1, 2, 3, 4], = 4. 

we directly specify list sub-goal of our query,

11 ?- list1 = [1,2,3,4], member(a,list1). list1 = [1, 2, 3, 4], = 1 ; list1 = [1, 2, 3, 4], = 2 ; list1 = [1, 2, 3, 4], = 3 ; list1 = [1, 2, 3, 4], = 4. 

making use of predicate =/2, opposed redefining it, is forbidden.

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the above answers 1). 2), aren't telling whole truth. appear have done, first make query

12 ?- list1 = [a,b,c,d]. list1 = [a, b, c, d]. 

which fine , dandy; , then make another query,

13 ?- member(a,list1). list1 = [a|_g2181] ; list1 = [_g2180, a|_g2184] ; list1 = [_g2180, _g2183, a|_g2187] ; list1 = [_g2180, _g2183, _g2186, a|_g2190] ; list1 = [_g2180, _g2183, _g2186, _g2189, a|_g2193] . 

prolog prompt not repl. don't make definitions @ it. make queries.