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tutorials:intermediate:json_prolog [2019/04/24 11:43] – [Importing a package with queries] gkazhoyatutorials:intermediate:json_prolog [2019/04/24 11:54] – [Case-sensitive variable names] gkazhoya
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 and if you check your terminal, in which the ''json_prolog'' node is running, there will be a huge java print as well, basically explaining the same thing. and if you check your terminal, in which the ''json_prolog'' node is running, there will be a huge java print as well, basically explaining the same thing.
      
-    + 
 +==== Case-sensitive variable names ==== 
 + 
 +In the former query we got a weird result from Prolog which looked like this:  
 +<code lisp> 
 +|''helloworld''| 
 +</code> 
 +What do the pipes stand for in this case? 
 + 
 +Lisp is case-insensitive, that means that variable of function names, or more correctly said, any symbol, can be written in any capitalization and will refer to the same symbol: 
 + 
 +<code lisp> 
 +CL-USER> (eq 'hello 'HELLO) 
 +T 
 +CL-USER> (eq 'hello 'Hello) 
 +T 
 +</code> 
 + 
 +Prolog, on the other hand, is case-sensitive. 
 +And in some cases, one would like to have a case-sensitive variable in Lisp as well. 
 +This is where the pipes come into play: 
 +<code lisp> 
 +CL-USER> (intern "HELLO") 
 +HELLO 
 +:INTERNAL 
 +CL-USER> (intern "Hello") 
 +|Hello| 
 +NIL 
 +</code> 
 +The function ''intern'' creates a symbol from a string. 
 +If the string is all capital, we get a normal usual symbol, in the other case we get the pipes. 
 + 
 +The same is with Prolog, if your variable or any other symbol is not all caps, you will get a symbol in Lisp which has pipes around it: 
 + 
 +<code lisp> 
 +CL-USER> (json-prolog:prolog-simple-1 "member(X, [1,2,3])") 
 +(((?X . 1))) 
 +CL-USER> (json-prolog:prolog-simple-1 "member(MYVAR, [1,2,3])") 
 +(((?MYVAR . 1))) 
 +CL-USER> (json-prolog:prolog-simple-1 "member(MY_VAR, [1,2,3])") 
 +(((?MY_VAR . 1))) 
 +CL-USER> (json-prolog:prolog-simple-1 "member(My_var, [1,2,3])") 
 +(((|?My_var| . 1))) 
 +</code> 
 + 
 +In that case, to get the value of the variable you should also use pipes: 
 + 
 +<code lisp> 
 +CL-USER> (cut:var-value '|?My_var| 
 +                        (car (json-prolog:prolog-simple-1 "member(My_var, [1,2,3])"))) 
 +1 
 +</code> 
 + 
 +Please note that in Prolog, all variables have to start with a capital letter and cannot contain dashes: 
 +<code lisp> 
 +CL-USER> (json-prolog:prolog-simple-1 "member(x, [1,2,3])") 
 +NIL 
 +CL-USER> (json-prolog:prolog-simple-1 "member(MY-VAR, [1,2,3])") 
 +NIL 
 +</code>
 ==== (NIL) vs NIL ==== ==== (NIL) vs NIL ====