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POError using string_to_atom: Arguments are not sufficiently instantiated
 

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  1. POError using string_to_atom: Arguments are not sufficiently instantiated
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    <p>I'm working on a URI parser in Prolog, but at the moment I'm stuck with something much simpler. I am exploring a string to find a particular char, ":", and when I find it, I want to have a string that only contains the concatenated chars before it.</p> <p>This program:</p> <pre><code>% caratteri speciali colonCheck(S) :- string_to_atom([S], C), C = ':'. % S==: headGetter([H|T], [H]) :- !. % struttura uri uri(Scheme, Userinfo, Host, Port, Path, Query, Fragment). % parsing uri parsed_uri(UriInput, uri(Scheme,Userinfo,Host,Port,Path,Query,Fragment)) :- scheme(UriInput, uri(S,Userinfo,Host,Port,Path,Query,Fragment)), not(headGetter(UriInput, ':')), !, string_to_atom([S], Scheme). % controllo Scheme, in ingresso ho i dati da controllare e l'oggetto uri che % mi servirà per inviarlo al passaggio successivo ho trovato i due punti scheme([H|T], uri(Scheme,Userinfo,Host,Port,Path,Query,Fragment)):- colonCheck(H), !, end(Scheme). % non trovo i due punti e procedo a controllare il prossimo carattere % (la testa dell'attuale coda) scheme([H|T], uri(Scheme,Userinfo,Host,Port,Path,Query,Fragment)):- not(colonCheck(H)), scheme(T, uri(This, Userinfo,Host,Port,Path,Query,Fragment)), append([H], This, Scheme). %fine computazione end([S]). </code></pre> <p>Gives this result:</p> <pre><code>?- scheme("http:", uri(A,_,_,_,_,_,_)). A = [104, 116, 116, 112, _G1205]. </code></pre> <p>I think that part is correct, but now I want to convert the char list into a string, so I changed the last line to this:</p> <pre><code>end([S]) :- string_to_atom([S], K). </code></pre> <p>But I get this error message:</p> <blockquote> <p>ERROR: string_to_atom/2: Arguments are not sufficiently instantiated</p> </blockquote> <p>I'm probably missing something. Can you tell what it is?</p>
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    1. CONote that in your "terminal" clause `end(Scheme)` of `scheme/2`, the rule for `end/1` creates a free variable. If that's what you intend, okay, but it seems to be the presence of that free variable causing the error in calling `string_to_atom/2`. Also a good idea is specifying which Prolog you are using, so any possible quirks can be discussed.
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    2. COWhat happens if you use: end([S]) :- print(S)
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    3. CO@hardmath: i'm usign swi-prolog
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