From: Markus Triska <triska@metalevel.at>
Date: Sat, 14 May 2022 06:09:01 +0000 (+0200)
Subject: FIXED: can_be(chars, [a,X]), i.e., if variables occur as elements
X-Git-Tag: v0.9.1~30^2~1
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=15cc916333d823ae11f2da9a0b78d5cd1de9f995;p=scryer-prolog.git

FIXED: can_be(chars, [a,X]), i.e., if variables occur as elements

This should simplify 2f3de51e554629d2e7b4ea023c9ef181c240692c and
other cases like it.
---

diff --git a/src/lib/error.pl b/src/lib/error.pl
index 68d7d3ee..a7cc4a5a 100644
--- a/src/lib/error.pl
+++ b/src/lib/error.pl
@@ -128,7 +128,11 @@ can_be(Type, Term) :-
 can_(integer, Term) :- integer(Term).
 can_(atom, Term)    :- atom(Term).
 can_(character, T)  :- character(T).
-can_(chars, Ls)     :- '$is_partial_string'(Ls).
+can_(chars, Ls)     :-
+        (   '$is_partial_string'(Ls) -> true
+        ;   can_be(list, Ls),
+            can_be_chars(Ls)
+        ).
 can_(list, Term)    :- list_or_partial_list(Term).
 can_(boolean, Term) :- boolean(Term).
 can_(term, Term)    :-
@@ -137,6 +141,12 @@ can_(term, Term)    :-
         ;   type_error(term, Term, can_be/2)
         ).
 
+can_be_chars(Var) :- var(Var), !.
+can_be_chars([]).
+can_be_chars([X|Xs]) :-
+        can_be(character, X),
+        can_be_chars(Xs).
+
 list_or_partial_list(Ls) :-
         '$skip_max_list'(_, _, Ls, Rs),
         (   var(Rs) -> true