# Term\_expansion/2 to make Prolog syntax look more like classical FOL **URL:** \ **Category:** Help!\ **Created:** [March 13, 2019, 11:30am UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389 "2019-03-13T11:30:19Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![JCR](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@JCR](https://swi-prolog.discourse.group/u/JCR)\ **Post date:** [March 13, 2019, 11:30am UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/1 "2019-03-13T11:30:19Z")
Hi! I am trying to get Prolog code look more like FOL, and I used op/3 and term\_expansion/2 to do this. ```auto :- op(1200, xfx, ==>). :- op(1000, xfy, /\). :- op(1100, xfy, \/). term_expansion(A ==> B, B:- A). term_expansion(A /\ B, A, B). term_expansion(A \/ B, A; B). man(X) /\ unmarried(X) ==> bachelor(X). man(john). man(peter). unmarried(john). main:-bachelor(X), writeln(X), nl, fail. ``` But i get the error ERROR: bachelor/1: Undefined procedure: (/)/2 Exception: (5) man(\_1740)/\unmarried(\_1740) ? Can anyone help? Thanks! ---
**Author:** ![EricGT](https://avatars.discourse-cdn.com/v4/letter/e/f1d935/32.png) [@EricGT](https://swi-prolog.discourse.group/u/EricGT)\ **Post date:** [March 13, 2019, 12:00pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/2 "2019-03-13T12:00:20Z")
It is great that are making use of both StackOverflow and this site. It might help others if you included links to your previous [questions](https://stackoverflow.com/users/3170496/jcr) so they can see the history. 🙂 ---
**Author:** ![CapelliC](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/capellic/32/17_2.png) [@CapelliC](https://swi-prolog.discourse.group/u/CapelliC)\ **Post date:** [March 13, 2019, 1:06pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/3 "2019-03-13T13:06:38Z")
Note you’re missing parenthesis in your term\_expansion clauses. After I corrected them, still /\ and \/ weren’t expanded, so maybe… ```auto :- module(fol, [main/0]). :- op(1200, xfx, ==>). :- op(1000, xfy, /\). :- op(1100, xfy, \/). term_expansion(A ==> B, B:- A). goal_expansion(A /\ B, (A, B)). goal_expansion(A \/ B, (A; B)). man(X) /\ unmarried(X) ==> bachelor(X). man(john). man(peter). unmarried(john). main:-bachelor(X), writeln(X), nl, fail. ``` It yields an answer now: ```auto ?- main. john ``` ---
**Author:** ![JCR](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@JCR](https://swi-prolog.discourse.group/u/JCR)\ **Post date:** [March 13, 2019, 2:00pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/4 "2019-03-13T14:00:59Z")
Thanks, perfect. ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [March 13, 2019, 2:17pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/5 "2019-03-13T14:17:09Z")
> [@JCR](#): > > :- op(1200, xfx, ==\>). :- op(1000, xfy, /). :- op(1100, xfy, /). If do it nice you do of course like this 🙂 ```prolog :- op(1200, xfx, ⇒). :- op(1000, xfy, ∧). :- op(1100, xfy, ∨). ``` ---
**Author:** ![JCR](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@JCR](https://swi-prolog.discourse.group/u/JCR)\ **Post date:** [March 13, 2019, 4:01pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/6 "2019-03-13T16:01:50Z")
@jan Even better 🙂 But i got the error “Illegal character” using ⇒, ∧, and ∨. By they way, thank you very much for making SWI! ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [March 13, 2019, 4:15pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/7 "2019-03-13T16:15:53Z")
You need Unicode support. The above works fine on my Ubuntu machine which since long defaults to using UTF-8. SWI-Prolog picks up the default locale, at least on most Unix-like systems. So, what is your setup? OS? Locale settings? Editor? It may all matter. You get a reliable result on any system if you can use an editor that can add a Unicode BOM marker at the start of the file. You can find Prolog’s idea of the encoding using ``` ?- current_prolog_flag(encoding, E). ``` That is either some encoding name or `text`, meaning it doesn’t understand what the encoding is, but it relies on the C library to translate the input and output to Unicode. ---
**Author:** ![JCR](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@JCR](https://swi-prolog.discourse.group/u/JCR)\ **Post date:** [March 13, 2019, 4:18pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/8 "2019-03-13T16:18:33Z")
> [@jan](#): > > ?- current\_prolog\_flag(encoding, E). Aha, OK. I get E = text. in response to the current\_prolog\_flag query. I have MacOs 10.13.6 and use Sublime text as an editor (and to run code). ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [March 13, 2019, 4:29pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/9 "2019-03-13T16:29:40Z")
Now things get complicated ☹ It differs whether using the window app from the binary distribution or the `swipl` console app. Otherwise I just hope someone has the answer. I only have a 12 year old Mac on which I (very slowly) compile SWI-Prolog … ---
**Author:** ![JCR](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@JCR](https://swi-prolog.discourse.group/u/JCR)\ **Post date:** [March 13, 2019, 5:54pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/10 "2019-03-13T17:54:43Z")
I’ll probably find some solution, thanks for your help! ---
**Author:** ![JCR](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@JCR](https://swi-prolog.discourse.group/u/JCR)\ **Post date:** [August 29, 2019, 8:12pm UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/11 "2019-08-29T20:12:01Z")
For the sake of completeness, here is an example that brings together your suggestions: ``` :- op(1200, xfx, ⇒). :- op(1000, xfy, ∧). :- op(1100, xfy, ∨). :- op(900, fy, ¬). term_expansion(A ⇒ B, B:- A). goal_expansion(A ∧ B, (A, B)). goal_expansion(A ∨ B, (A; B)). goal_expansion(¬A, \+A). man(john). unmarried(mark). unmarried(X) ∧ man(X) ⇒ bachelor(X). main:-unmarried(X), writeln(X). ``` The solution to the Illegal character error in Sublime text is: using Save with Encoding -\> UTF-8 with BOM in Sublime text. ---
**Author:** ![grossdan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/grossdan/32/23_2.png) [@grossdan](https://swi-prolog.discourse.group/u/grossdan)\ **Post date:** [August 30, 2019, 4:18am UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/12 "2019-08-30T04:18:39Z")
On linked-in someone asked to provide examples of code for counting from one to twenty. I decided to add the following code, while encouraging a declarative reading: forall(between(1,20,X), writeln(X)). However, someone then asked from where the order comes from. Which actually showed how the procedural reading “lurks” behind the scene … Dan ---
**Author:** ![CapelliC](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/capellic/32/17_2.png) [@CapelliC](https://swi-prolog.discourse.group/u/CapelliC)\ **Post date:** [August 30, 2019, 5:25am UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/13 "2019-08-30T05:25:05Z")
> [@grossdan](#): > > someone then asked from where I understand that person, by myself did the same question, and was amazed by the implementation 🙂 . Then, library(aggregate) with foreach/2 come into play. Maybe that’s more an interesting showcase of a round trip into procedural programming. ---
**Author:** ![grossdan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/grossdan/32/23_2.png) [@grossdan](https://swi-prolog.discourse.group/u/grossdan)\ **Post date:** [August 30, 2019, 5:58am UTC](https://swi-prolog.discourse.group/t/term-expansion-2-to-make-prolog-syntax-look-more-like-classical-fol/389/14 "2019-08-30T05:58:30Z")
> [@CapelliC](#): > > Maybe that’s more an interesting showcase of a round trip into procedural programming. Here is a trial without assuming order … bagof(X, between(1,20,X), Xs), sort(Xs, SortedXs), maplist(writeln, SortedXs). Although, it is declarative, somehow the declarative reading is lost … i like the use of forall hinting at the universal quantifier – the term sort is in imperative language – and maplist is also imperative in flavor … Dan