Re: Tcl Switch case

On 19 feb, 10:02, "MartinLemburg@Siemens-PLM"
<martin.lemburg.siemens-...@xxxxxxx> wrote:
Hi Andreas,

while willing to agree, that this 8.5(.x) change (it works in 8.5.0,
too) equalizes the behaviour of such commands like lsearch, switch,
etc.:

    % lsearch -hello *hello
    0
    % switch -hello {-hello {expr {0}}}
    0

But I'm not willing to accept it as feature if syntactical elements
are handled like you showed:

    % switch -- {-- {expr {0}}}
    0

This is definitely (IMHO) an error, because "--" signals the end of
the options and that the next argument is the string to be used with
the switch cases.

It should behave like e.g. ...

    % glob --; # could have returned an empty list
    wrong # args: should be "glob ?switches? name ?name ...?"

    % regexp -- ----; # could have return 1
    wrong # args: should be "regexp ?switches? exp string ?matchVar? ?
subMatchVar subMatchVar ...?"

    % regsub -- ---- !; # could have returned "!!"
    wrong # args: should be "regsub ?switches? exp string subSpec ?
varName?"

So - no matter how far switch is nearer to e.g. lsearch in its syntax,
it is now much far away from the syntax of "--" accepting commands.

Best regards,

Martin

P.S.: I never understood, why such syntactical differences are between
e.g. lsort and e.g. switch. The first accepts any "-\w+" pattern as
data, if it is no valid option, the last throws an error if an "-\w+"
argument is not a valid option. What's about equalizing option
accepting commands?

On 18 Feb., 21:30, Andreas Leitgeb <a...@xxxxxxxxxxxxxxxxxxxxxxxx>
wrote:

Donald Arseneau <a...@xxxxxxxxx> wrote:
On Feb 18, 7:43 am, Mark Janssen <mpc.jans...@xxxxxxxxx> wrote:
Or use the stable Tcl 8.5.1. 8.5.1 recognizes that with [switch $a
$body], $a cannot be a flag so it will not try to interpret it as one..
WHAT!?!?  That breaks Tcl's parser rules.

nothing actually does.

The $a must be substituted
before the switch command has any effect -- it (switch) can only see
the resulting text that came out of $a.

What you say is true, but who spoke against it?

switch -- {-- {puts ok}}

Of course also prints "ok" to stdout (with 8.5.1 and up), so no
discrimination between $,[] and constant values is happening.
It's the number of args, that prevents "switch $a $body" from
taking $a for an option, not whether they're constant or not.

I certainly agree that the option handling of Tcl commands is a bit
inconsistent between commands. One of the things I would like to see
addressed in Tcl9 is making option handling in Tcl more uniform and
providing an easier way to add the same handling in your own procs.

I was thinking about using for instance a dict to pass options, but I
am not sure I really like the syntax that would lead to e.g.

lsearch {-inline 1 -all 1} list pattern

all commands would then have the general form:

command ?options? arg1 arg2 arg3 .....

This also has the advantage of removing the need for -- to signify the
end of the options. Determining if any options have been specified
reduces to simple argument counting for all commands.

Mark
.

Relevant Pages

  • Re: Tcl Switch case
    ... too) equalizes the behaviour of such commands like lsearch, switch, ...
    (comp.lang.tcl)
  • Re: Tcl Switch case
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