Amb: Difference between revisions

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 =={{Header|SETL}}==
+<lang SETL>program amb;
+sets := unstr('[{the that a} {frog elephant thing} {walked treaded grows} {slowly quickly}]');
+words := [amb(words): words in sets];
+if exists lWord = words(i), rWord in {words(i+1)} |
+          lWord(#lWord) /= rWord(1) then
+  fail;
+end if;
+proc amb(words);
+  return arb {word in words | ok};
+end proc;
+end program;</lang>
+Sadly ''ok'' and ''fail'' were only ever implemented in CIMS SETL, and are not in any compiler or interpreter that is available today, so this is not very useful as it stands.
+===Alternate version (avoids [http://www.setl-lang.org/wiki/index.php/Backtracking backtracking])===
 <lang SETL>program amb;
@@ Line 339: / Line 357: @@
 end program;</lang>
+We cheat a bit here - this version of ''amb'' must be given the whole list of word sets, and that list is consumed recursively.  It can't pick a word from an individual list.
-===Alternate version (uses [http://www.setl-lang.org/wiki/index.php/Backtracking backtracking])===
-<lang SETL>program amb;
-sets := unstr('[{the that a} {frog elephant thing} ' +
-              '{walked treaded grows} {slowly quickly}]');
-print(amb(sets));
-proc amb(sets);
-  sentence := [];
-  (for words in sets)
-    if exists word in words |
-              ok and (sentence = [] or
-                      word(1) = (reverse sentence(#sentence))(1)) then
-      sentence with:= word;
-    else
-      fail;
-    end if;
-  end;
-  return sentence;
-end proc;
-end program;</lang>