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tutorials:intermediate:json_prolog [2019/04/24 11:46] – gkazhoya | tutorials:intermediate:json_prolog [2020/06/11 11:52] – [Prerequisites] removed the previos commit - wrong tutorial. sorry. hawkin | ||
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This tutorial requires CRAM, roslisp_repl and ROS to have already been installed. Go through the previous tutorials and the installation page if you don't have CRAM installed yet. | This tutorial requires CRAM, roslisp_repl and ROS to have already been installed. Go through the previous tutorials and the installation page if you don't have CRAM installed yet. | ||
Make sure you have **Java 8** and **Gradle 5.1** already installed. Otherwise you won't be able to build KnowRob. Other versions could work, but have not been tested yet, so use them at your own risk! | Make sure you have **Java 8** and **Gradle 5.1** already installed. Otherwise you won't be able to build KnowRob. Other versions could work, but have not been tested yet, so use them at your own risk! | ||
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=== Installation === | === Installation === | ||
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==== Case-sensitive variable names ==== | ==== Case-sensitive variable names ==== | ||
- | In the former query we got a weird result from Prolog which looked like this: '' | + | In the former query we got a weird result from Prolog which looked like this: |
+ | <code lisp> | ||
+ | |'' | ||
+ | </ | ||
+ | What do the pipes stand for in this case? | ||
+ | Lisp is case-insensitive, | ||
+ | <code lisp> | ||
+ | CL-USER> (eq 'hello ' | ||
+ | T | ||
+ | CL-USER> (eq 'hello ' | ||
+ | T | ||
+ | </ | ||
+ | |||
+ | 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 | ||
+ | :INTERNAL | ||
+ | CL-USER> (intern " | ||
+ | |Hello| | ||
+ | NIL | ||
+ | </ | ||
+ | The function '' | ||
+ | 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: | ||
+ | (((?X . 1))) | ||
+ | CL-USER> (json-prolog: | ||
+ | (((?MYVAR . 1))) | ||
+ | CL-USER> (json-prolog: | ||
+ | (((?MY_VAR . 1))) | ||
+ | CL-USER> (json-prolog: | ||
+ | (((|? | ||
+ | </ | ||
+ | |||
+ | In that case, to get the value of the variable you should also use pipes: | ||
+ | |||
+ | <code lisp> | ||
+ | CL-USER> (cut: | ||
+ | (car (json-prolog: | ||
+ | 1 | ||
+ | </ | ||
+ | |||
+ | Please note that in Prolog, all variables have to start with a capital letter and cannot contain dashes: | ||
+ | <code lisp> | ||
+ | CL-USER> (json-prolog: | ||
+ | NIL | ||
+ | CL-USER> (json-prolog: | ||
+ | NIL | ||
+ | </ | ||
==== (NIL) vs NIL ==== | ==== (NIL) vs NIL ==== | ||
| |