( i * x fileid -- j * x )

Remove fileid from the stack. Save the current input source specification, including the current value of SOURCE-ID. Store fileid in SOURCE-ID. Make the file specified by fileid the input source. Store zero in BLK. Other stack effects are due to the words included.

Repeat until end of file: read a line from the file, fill the input buffer from the contents of that line, set >IN to zero, and interpret.

Text interpretation begins at the file position where the next file read would occur.

When the end of the file is reached, close the file and restore the input source specification to its saved value.

An ambiguous condition exists if fileid is invalid, if there is an I/O exception reading fileid, or if an I/O exception occurs while closing fileid. When an ambiguous condition exists, the status (open or closed) of any files that were being interpreted is implementation-defined.



Here are two implementation alternatives for saving the input source specification in the presence of text file input:

  1. Save the file position (as returned by FILE-POSITION) of the beginning of the line being interpreted. To restore the input source specification, seek to that position and re-read the line into the input buffer.

  2. Allocate a separate line buffer for each active text input file, using that buffer as the input buffer. This method avoids the "seek and reread" step, and allows the use of "pseudo-files" such as pipes and other sequential-access-only communication channels.