1. Fw: Re: goto's, and loops
-----Original Message-----
From: Ralf Nieuwenhuijsen <nieuwen at xs4all.nl>
To: Derek Parnell <dparnell at bigpond.net.au>
Date: Friday, July 30 1999 03:42
Subject: Re: Re: goto's, and loops
|I really wouldn't mind such a contruct to be added to Euphoria.
|It allows exiting to block-constructs, but it the ability to name such a
|construct also allows the interpreter to optimize the block as a whole,
it
|could allow for even more local variables and it would greatly improve
the
|readability for three reasons:
|
| 1) You don't have to comment the use of a block you _name_ it.
| 2) You don't have to use exitflags
| 3) You don't have to use goto
|
|Implementation-wise, I would suggest to allow to name each statements
(great
|for looking up in editors as well, the name is ignored by the
interpreter,
|unless its a loop construct, in which case you can use it to specify how
|many levels to jump)
|
|And btw, consider the error message, (which is worth the trouble alone):
|
|" An error has occurding during tokenizing at line 123 "
|
|Example code:
|-- Notice the fact that the whitespace function is not part of the other
|routine because it
|-- can be used much more often. Sometimes routines are a better choice,
|sometimes they
|-- are not.
|
|include common.e -- aka Eu-Upgrade-Library .. its at my site, webgen
|needs it as well
|
|global function whitespace (sequence s)
| return (s = ' ') + (s = '\n') + (s = '\t') + (s = '\r')
|end function
|
|global function parse_file (sequence fname)
|sequence tok, ct, mask
|integer fh
|
| reading file: -- It is used as a comment here, but why not ?
| fh = open (fname, "r")
| if fh = NONE then
| return NONE
| end if
|
| init: tok = {} ct = "" mask = whitespace (cl)
| tokenizing: for index = 1 to length (mask) do
|
| if mask[index] then
| if length(ct) then
| tok = append(tok, ct)
| ct = ""
| end if
| else
| ct = append(ct, cl[index])
| end if
|
| end tokenizing
|
| .. more code ..
|
|end function
|
|--------
|
|I really do suspect this can help the interpreter optimizing. If it has
to
|slow down, or clean cache or whatever, which is not really needed
|immediately, it can wait until the next 'named' part of code. In between,
is
|the best place for unnatural pauses. Rather than inside the loop
construct
|every now and so often. Also in windows, which I know is preemtive, it
can
|help keep the natural flow, for example by increasing the priority during
|the block, and then releasing it at the end of such a block. It would
then
|never slow down during a draw procces, but inbetween, etc. timing can
make
|so much difference .. I think.
|
|Ralf N.
|nieuwen at xs4all.nl
|
|[[ The elevator ]]
|Http://www.xs4all.nl/~nieuwen
|
|Derek wrote:
|> Another language I use, Progress 4GL, has a specialized variety of
goto.
|> It uses the syntax "leave <blockname>" . Your example would be coded
|> thus...
|>
|> loop1: repeat:
|> some code
|> loop2: repeat:
|> if var then leave loop1.
|> end. /* of loop2 */
|> more code
|> end. /* of loop 1 */
|>
|> The idea of named blocks of code might not be too difficult it add to
|> Euphoria, however name-space issues might arise.
|>
|>
|> cheers,
|> Derek Parnell
|> dparnell at bigpond.net.au
|> Melbourne, Australia
|>
|
|
