On 2018-04-28 18:16, Tim Peters wrote: > [Steven D'Aprano <st...@pearwood.info>] >> But the biggest problem is that this re-introduces exactly the same >> awful C mistake that := was chosen to avoid. Which of the following two >> contains the typo? >> >> local(spam=expression, eggs=expression, cheese = spam+eggs) >> >> local(spam=expression, eggs=expression, cheese == spam+eggs) > > [snip] > > Still, if people are scared of that, a variation of Yury's alternative > avoids it: the last "argument" must be an expression (not a binding). > In that case your first line above is a compile-time error. > > I didn't like that because I really dislike the textual redundancy in the > common > > if local(matchobject=re.match(regexp, line), matchobject): > > compared to > > if local(matchobject=re.match(regexp, line)): > > But I could compromise ;-) > > - There must be at least one argument. > - The first argument must be a binding. > - All but the last argument must also be bindings. > - If there's more than one argument, the last argument must be an expression.
How about if you just can't have an expression in a local()? There are a
few obvious alternative possibilities:
1. No special case at all:
local(x=1, y=2, _=x+y)
2. Co-opt a keyword after local():
local(x=1, y=2) in x+y
3. Co-opt a keyword inside local():
local(x=1, y=2, return x+y)
I hate the first and wish the _ pattern would die in all its forms, but
it's worth mentioning. I don't think there's much to choose between the
other two, but 2 uses syntax that might have been valid and meant
something else, so 3 is probably less confusing.
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