list - Prolog code gives two different results -


so i'm making code there's function receives 2 arguments , tells if 1 of them not list.

the code following:

/*** list check ***/ islist(l) :- l == [], !. islist(l) :- nonvar(l), aux_list(l). aux_list([_|_]).  /*** double list check ***/ double_check(l, l1) :- \+islist(l) -> write("list 1 invalid");      \+islist(l1)-> write("list 2`invalid"); write("success").

it shuold working. online code want to. on prolog console of computer gives different answer:

?- double_check(a, [a]). [76,105,115,116,97,32,49,32,105,110,118,97,108,105,100,97]  true.

example. have no idea list came from. can tell me error , me fix please? thank all!

quick fix: use format/2 instead of write/1! more information on built-in predicate format/2, click here.

$ swipl --traditional welcome swi-prolog (multi-threaded, 64 bits, version 7.1.37) [...]  ?- write("abc"). [97,98,99]                                % output write/1 via side-effect true.                                     % truth value of query (success)  ?- format('~s',["abc"]). abc                                       % output format/2 via side-effect true.                                     % truth value (success)

however different command line arguments:

$ swipl  welcome swi-prolog (multi-threaded, 64 bits, version 7.1.37) [...]  ?- write("abc"). abc true.  ?- format('~s',["abc"]). abc true.

even though may seem nuisance, recommend using command-line option --traditional swi-prolog, in combination format/2 instead of write/1. preserve !


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