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From: darrylo@hpnmdla.HP.COM (Darryl Okahata)
Newsgroups: comp.sys.handhelds
Subject: Unix-link PATH searching for the HP-48SX
Message-ID: <1570006@hpnmdla.HP.COM>
Date: 11 Jul 90 20:20:39 GMT
Organization: HP Network Measurements Div, Santa Rosa, CA
Lines: 106


     Here is yet another method for accessing programs in other
directories.  It introduces the concept of a Unix-like "PATH" variable,
which gives a list of directories to search.  This program, called
"EXEC", works just like Jan Christiaan van Winkel's (jc@atcmp.nl) SVC
function, except that it will search multiple paths.  You enter the
arguments to your function on the stack, enter the name of your function
(e.g., 'MYFUNC'), and then execute "EXEC".

     To use it, you need a variable called "EXECPATH" in the HOME
directory, and this variable should contain a list of directory paths
(in list form).  For example, one possible value for EXECPATH could be:

	{ { SYS } { ETC } { ETC ETC } HOME { } }

This causes EXEC to search the following directories for functions:

	{ SYS }
	{ ETC }
	{ ETC ETC }
	HOME
	the current working directory

Note that HOME does not have to be in a list (for that matter, directory
paths with only one name do not have to be in a list, but it makes it
easier to debug).  Also note that placing HOME in this list is
redundant; as everything searches HOME, HOME should never be placed in
this list.


Notes/problems:

1. EXECPATH does not necessarily come from the HOME directory.  Strange
   things will happen if EXECPATH resides in the "current directory" or
   in one of the directories given by EXECPATH.

2. The name "EXECPATH" is too long.  It should be shortened to save
   time and space.

3. EXEC is slow.  The overhead in using EXEC is at least 0.1 sec (I
   don't know what the overhead in using SVS is, however).  The actual
   overhead depends on how large and complex your EXECPATH happens to
   be.  EXEC should be rewritten in assembly language.  It should,
   perhaps, keep more things on the stack and not in local variables.

4. EXEC is big (240 bytes).

5. If "{ }" is not contained in the EXECPATH list, the current working
   directory will not be searched.

6. Some people will want to remove the code that handles "{ }" (searches
   the current working directory).  This will increase speed and
   decrease program size.  To do this, replace the lines that say:

		IF DUP SIZE 0
	==
		THEN DROP cwd
		END EVAL

   with:

		EVAL

7. Searching HOME is redundant.


     -- Darryl Okahata
	UUCP: {hplabs!, hpcea!, hpfcla!} hpnmd!darrylo
	Internet: darrylo%hpnmd@hp-sde.sde.hp.com

DISCLAIMER: this message is the author's personal opinion and does not
constitute the support, opinion or policy of Hewlett-Packard or of the
little green men that have been following him all day.


===============================================================================
Store the following in a variable called "EXEC" in the HOME directory.
Checksum: #19683d
-------------------------------------------------------------------------------
%%HP: T(3)A(D)F(.);
\<< PATH EXECPATH
SIZE 1 \-> cwd end i
  \<<
    DO EXECPATH i
GET
      IF DUP SIZE 0
==
      THEN DROP cwd
      END EVAL
      IF
        IFERR RCL 1
        THEN
          IF 'i'
INCR end >
          THEN cwd
EVAL " :NOT FOUND"
+ DOERR
          END 0 0
        END
      THEN cwd EVAL
EVAL 1
      END
    UNTIL
    END
  \>>
\>>