Node:Syntax Errors, Next:Undefined Predicates, Previous:Queries and Directives, Up:Run Intro
Syntax errors are detected during reading. Each clause, directive or in
general any term read in by the built-in predicate read/1 that
fails to comply with syntax requirements is displayed on the standard
error stream as soon as it is read, along with its position in the input
stream and a mark indicating the point in the string of symbols where
the parser has failed to continue analysis, e.g.:
| member(X, X$L). ! Syntax error ! , or ) expected in arguments ! in line 5 ! member ( X , X ! <<here>> ! $ L ) .
if $ has not been declared as an infix operator.
Note that any comments in the faulty line are not displayed with the error
message. If you are in doubt about which clause was wrong you can use the
listing/1 predicate to list all the clauses which were successfully
read in, e.g.
| ?- listing(member/2).
NOTE: The built in predicates read/[1,2] normaly raise an exception
on syntax errors (see Exception). The behavior is controlled by the
flag syntax_errors (see prolog_flag/3).