System Streams

  Apart from stream names defined by the user, ECLiPSe also contains 13 predefined logical system streams. At the beginning of a session they are assigned to the standard UNIX streams, but they can be changed by the user, except for those which must not be modified. The system streams are:  

input

Used by the input predicates that do not have the stream as an explicit argument, e.g. read/1.    

output

Used by the output predicates that do not have the stream as an explicit argument, e.g. write/1.    

error

Output for error messages and warnings and all messages about exceptional states.  

toplevel_input

The input for the top-level Prolog loop, it reads the user query and the semicolon or newline typed to indicate whether other solutions are required.    

toplevel_output

The messages from the top-level loop, e.g. the yes/no   answer, delayed goals, messages about loaded libraries.  

answer_output

Outputs the top-level loop answer bindings for the user query.  

debug_input

Input to the debugger.  

debug_output

Output from the debugger  

null

  A dummy stream, output to it is discarded, on input it always gives end of file. It can be used to ignore part of a program's output without having to remove the output predicates. Note that this stream is similar to the UNIX file '/dev/null' but works much faster. This stream cannot be redirected to any other physical stream.

set_prompt(InputStream, Prompt, OutputStream)

Apart from these system streams there are other logical stream identifiers provided by the system:

stdin

  The UNIX standard input stream when the ECLiPSe session is started.

stdout

  The UNIX standard output stream when the ECLiPSe session is started.

stderr

  The UNIX standard error output stream when the ECLiPSe session is started.

user

  This identifier is provided for compatibility with other Prolog systems and it is identical with stdin and stdout depending on the context where it is used. When it is not possible for the system to decide whether the input or output stream was meant by user, an exception is raised. This stream cannot be redirected to another physical stream.

When an attempt is made to close a system stream, the exception 196 is raised. The default handler for this exception resets all system streams connected with this physical streams to their defaults and then the physical stream is closed.

When set_stream(Logical_Stream, Stream) is used to redirect a system stream, Stream must have a mode compatible with that of Logical_Stream. That is, if Logical_Stream specifies a stream with read mode, Stream must have either read or update mode; if Logical_Stream has write mode, Stream must have either write, append or update mode; and if Logical_Stream has update mode, Stream must have update mode.