Ian Kelly <ian.g.ke...@gmail.com>:
> On Apr 4, 2014 3:51 AM, "Marko Rauhamaa" <ma...@pacujo.net> wrote:
>> switch: local_sabbath()
>> case (1, 2, 3) as sabbath:
>> ...
>> case 6:
>> ...
>> else:
>> ...
> [...]
>
> What's wrong with the much more natural "switch local_sabbath():"?
Consider:
switch local_sabbath(): # bad
case (1, 2, 3) as sabbath:
...
Now Python "framing" requires that you place something between the first
":" and "case":
switch local_sabbath(): # bad
pass
case (1, 2, 3) as sabbath:
...
Placing the expression after the colon terminates the first colon
cleanly. Also, the "lambda" precedent allows an expression to follow a
colon; both "lambda" and my "switch" mandate that the expression stay on
the same line with the colon.
> Second, "as" clauses are used in other contexts for local assignment.
> What is the purpose of doing that here? How does this solve the
> problem of explicitly denoting case multiplicity?
The "as" clause follows the precedent of the "try/except" statement. It
removes the occasional annoyance in C:
switch (next_char()) {
case '\n':
case '\r':
putchar(???);
: : :
which forces you to introduce a temporary variable:
char c;
: : :
c = next_char();
switch (c) {
case '\n':
case '\r':
putchar(c);
: : :
It is most useful in the "default"/"else" branch:
switch: q.pop()
case 0:
log_direction(0)
return 1
case (90, 270) as angle:
log_direction(angle)
return 0
case 180:
log_direction(180)
return -1
else angle:
log_direction(angle)
return math.cos(angle * 2 * PI / 360)
Marko
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