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streams.pl -- Manage Prolog streams |
This library provides high level primitives for stream operations. It is related to the charsio.pl and codesio.pl libraries. Considering these are de-facto standard Prolog libraries we prefer to leave these untouched.
current_output
, user_output
and user_error
) in the string
Output. Options processed:
[]
, causing the
predicate to call with_output_to/2. The only admissible
list elements are the alias names for the Prolog standard
streams. As current_output
is always captured, the only
two values are user_output
and user_error
true
, pretend the output is a terminal, causing messages
to use ANSI term escape sequences for color.For example, the following captures an error message. Note that we must catch and print the message inside Goal. If we do not do so the exception of Goal is simply propagated into the environment without binding Output.
?- with_output_to(string(Out), catch(A is log(-1), E, print_message(error, E)), [capture([user_error]), color(true)]). Out = "\u001B[1;31mERROR: is/2: Arithmetic: \c evaluation error: `undefined'\n\u001B[0m", E = error(evaluation_error(undefined), context(system:(is)/2, _)).