GAP's "ReadNC" command

GAP does not allow more than one line of comments using the usual "Read" command. For debugging and for adding examples to help remember proper synatx, multi-line comments would be very useful.

Thanks to a new command "ReadNC" written by Frank Luebeck, you can include multi-line comments into your file. This web page explains how to use the "ReadNC" command.

"ReadNC" reads files, possibly with comments inside a '%COMMENT' - '%ENDCOMMENT' block, in the following sense:
Any line beginning %COMMENT will be ignored as will all subsequent lines up to and including a matching %ENDCOMMENT line (i.e., a %COMMENT and %ENDCOMMENT block).

Example: Download ReadNC_example.gap or, enter the following text into a file called "ReadNC_example.gap", and save to your computer. (Unless it is saved to "/home/wdj/gapfiles/ReadNC_example.gap" you will have to modify the path below slightly.)

######################### begin ReadNC_example.gap##############################
Read("/home/wdj/gapfiles/ReadNC.gap"); #replace by your own path to ReadNC.gap

Print("\n This examples tests `Read` and `ReadNC` in GAP.\n");

%COMMENT

Print("\n But GAP does not read commands within %COMMENT - %ENDCOMMENT blocks.\n");

%ENDCOMMENT

Print("\n GAP reads commands outside %COMMENT - %ENDCOMMENT blocks.\n\n");
######################### end ReadNC_example.gap#################################

To test the ReadNC command, try both

Read("/home/wdj/gapfiles/ReadNC_example.gap");

(this will return some GAP syntax error messages) and

ReadNC("/home/wdj/gapfiles/ReadNC_example.gap");

in GAP. You should have the following output:


gap> Read("/home/wdj/gapfiles/ReadNC_example.gap");

 This examples tests `Read` and `ReadNC` in GAP.
Syntax error: expression expected in /home/wdj/gapfiles/ReadNC_example.gap line 21
%COMMENT
^
Syntax error: expression expected in /home/wdj/gapfiles/ReadNC_example.gap line 25
%ENDCOMMENT
^
gap> ReadNC("/home/wdj/gapfiles/ReadNC_example.gap");

 This examples tests `Read` and `ReadNC` in GAP.

 GAP reads commands outside %COMMENT - %ENDCOMMENT blocks.

true
gap> Read("/home/wdj/gapfiles/ReadNC_example.gap");

 This examples tests `Read` and `ReadNC` in GAP.

 GAP reads commands outside %COMMENT - %ENDCOMMENT blocks.

Notice that the second print command in read_example.gap was not executed since it was within a %COMMENT-%ENDCOMMENT block.

To start using this command, download the file: ReadNC.gap to a directory on your computer (unless it is "/home/wdj/gapfiles" you will have to modify the path below slightly). When you wish to use it, first type the following command into GAP.

Read("/home/wdj/gapfiles/ReadNC.gap");

If you simply add the above line to your .gaprc file then the new "ReadNC" command will be ready next time you start GAP.

wdj@usna.edu

Last updated 12-27-2004.

This page is at the url: http://cadigweb.ew.usna.edu/~wdj/gap/read_no_comments.html