How to deal with [a,b|c] format lists?

I created a simple parser for subset of Clojure language. For some reason it returns me a list in format [a,b,c|d], not in format [a,b,c,d]. Morover member(X, List) doesn't work with such format of list properly, i.e.

member(X, [a,b,c|d]).
X = a ;
X = b ;
X = c.

The question is how should I improve my code to fix this problem and get list in usual format ? Or maybe there is a way to transform [a,b,c|d] -> [a,b,c,d] ?

You can call e.g.

main.
[(concat x) (lambda x (inc (inc x)))]

And get:

expr([expr([expr(at(id([c,o,n,c,a,t])))|expr(at(id([x])))])|expr([expr(at(id([l,a,m,b,d,a]))),expr(at(id([x])))|expr([expr(at(id([i,n,c])))|expr([expr(at(id([i,n,c])))|expr(at(id([x])))])])])])

Code:

mydelimiter --> delimiter.
mydelimiter --> delimiter, mydelimiter.
delimiter --> [','].
delimiter --> ['\n'].
delimiter --> ['\t'].
delimiter --> ['\s'].

specsymbol('+') --> ['+'].
specsymbol('-') --> ['-'].
specsymbol('>') --> ['>'].
specsymbol('<') --> ['<'].
specsymbol('=') --> ['='].
specsymbol('*') --> ['*'].
specsymbol('_') --> ['_'].

snum(0) --> ['0'].
snum(1) --> ['1'].
snum(2) --> ['2'].
snum(3) --> ['3'].
snum(4) --> ['4'].
snum(5) --> ['5'].
snum(6) --> ['6'].
snum(7) --> ['7'].
snum(8) --> ['8'].
snum(9) --> ['9'].
numb([A]) --> snum(A).
numb([A|B]) --> snum(A), numb(B).
mynumber(num(X)) --> numb(X).

mystring(str([])) --> quotesymbol, quotesymbol.
mystring(str(S)) --> quotesymbol, anychars(S), quotesymbol.
quotesymbol --> ['\"'].
anychar(A) --> [A], {A \== '\"'}.
anychars([A]) --> anychar(A).
anychars([A|B]) --> anychar(A), anychars(B).

identifier(id(I)) --> id_start_spec(I); id_start_letter(I).
letter(L) --> [L], {is_alpha(L)}.
id_start_letter([L]) --> letter(L).
id_start_letter([L|I]) --> letter(L), ids_l(I).
ids_l([I]) --> letter(I); snum(I); specsymbol(I).
ids_l([I|Is]) --> (letter(I); snum(I); specsymbol(I)), ids_l(Is).
id_start_spec([S]) --> specsymbol(S).
id_start_spec([S|I]) --> specsymbol(S), ids_s(I).
ids_s([I]) --> snum(I); specsymbol(I).
ids_s([I|Is]) --> (snum(I); specsymbol(I)), ids_s(Is).

keyword(kw([C|K])) --> mycolonsymbol(C), id_start_letter(K).
mycolonsymbol(':') --> [':'].

myatom(at(A)) --> mynumber(A); mystring(A); identifier(A); keyword(A).

expression(expr(S)) --> myatom(S).
expression(expr(S)) --> r_br_expression(S).
expression(expr(S)) --> s_br_expression(S).
expression(expr(S)) --> f_br_expression(S).
r_br_expression(S) --> r_openbracketsymbol, expressions(S), r_closedbracketsymbol.
expressions(S) --> expression(S).
expressions([S|SS]) --> expression(S), mydelimiter, expressions(SS).
r_openbracketsymbol --> ['('].
r_closedbracketsymbol --> [')'].
s_br_expression(S) --> s_openbracketsymbol, expressions(S), s_closedbracketsymbol.
s_openbracketsymbol --> ['['].
s_closedbracketsymbol --> [']'].
f_br_expression(S) --> f_openbracketsymbol, expressions(S), f_closedbracketsymbol.
f_openbracketsymbol --> ['{'].
f_closedbracketsymbol --> ['}'].

main :-
    read_string(user_input, "\n", "", _, StrIn),
    atom_chars(StrIn, L),
    phrase(expression(T), L),
    writeln(T),
    !.

Solution 1:

First of all, use a better readable syntax, by setting the following directive in front of your code:

:- set_prolog_flag(double_quotes, chars).

Now you can write in stead of ['}'] the more compact "}", instead of ['\s'] the standard " ". Or specsymbol(+) --> "+". instead.

Second, define letter//1 and anychar//1 like so:

letter(L) --> [L], {char_type(L,alpha)}.

anychar(A) --> [A], {dif(A, '\"')}.

With this you can start to debug, best by using smaller test cases.

Also note that Prolog has a top level (prolog-toplevel), so there is no need to define main at all. Instead, you can type your query directly, or even better, consider a simpler case first:

?- phrase(expression(T),"(inc x)").
T = expr([expr(at(id("inc")))|expr(at(id("x")))]) 
?- phrase(expression(T),"(x)").
T = expr(expr(at(id("x"))))

So in the first case there is an odd instance of a partial list and in the second there is no list at all. Instead, both should be (well formed) lists. The culprit is expressions//1 which should rather read:

expressions([S]) --> expression(S).
expressions([S|Ss]) -->
   {Ss = [_|_]},   % redundant goal for termination
   expression(S), mydelimiter, expressions(Ss).

Note that also