* Case statement with ";|" [not implemented]
@ 2007-01-18 19:53 Gerald Lai
2007-01-19 4:52 ` Bart Schaefer
0 siblings, 1 reply; 3+ messages in thread
From: Gerald Lai @ 2007-01-18 19:53 UTC (permalink / raw)
To: zsh-users
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Hello all :)
I'm new to the mailing list.
I'm trying to convert the (simplified) code below to a case statement
structure:
===
if [[ $mycase -eq 0 ]]; then
echo "mycase is 0"
else
if [[ $mycase -eq 1 ]]; then
echo "mycase is 1"
else
echo "mycase is 2"
fi
echo "mycase is 1 or 2"
fi
===
And this is what I got:
===
case $mycase in
0)
echo "mycase is 0"
;;
1)
echo "mycase is 1"
;;
2)
echo "mycase is 2"
esac
if [[ $mycase -gt 0 ]] echo "mycase is 1 or 2"
===
My question is, shouldn't there be a way to do this:
===
case $mycase in
0)
echo "mycase is 0"
;;
1)
echo "mycase is 1"
;|
2)
echo "mycase is 2"
;|
*)
echo "mycase is 1 or 2"
esac
===
Note that ";|" provides an OR-like separator (as opposed to the AND-like
";&" separator) that goes through the case statements. However, unlike ";&",
it checks $mycase against 1) and 2) instead of blindly executing case
statements 1 & 2.
Wouldn't this be a good addition to ZSH? It certainly seems more useful than
";&".
--
Gerald Lai
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Case statement with ";|" [not implemented]
2007-01-18 19:53 Case statement with ";|" [not implemented] Gerald Lai
@ 2007-01-19 4:52 ` Bart Schaefer
2007-01-19 12:01 ` Peter Stephenson
0 siblings, 1 reply; 3+ messages in thread
From: Bart Schaefer @ 2007-01-19 4:52 UTC (permalink / raw)
To: zsh-users
On Jan 18, 11:53am, Gerald Lai wrote:
}
} My question is, shouldn't there be a way to do this:
} ===
} case $mycase in
} 0)
} echo "mycase is 0"
} ;;
}
} 1)
} echo "mycase is 1"
} ;|
}
} 2)
} echo "mycase is 2"
} ;|
}
} *)
} echo "mycase is 1 or 2"
} esac
} ===
} Note that ";|" provides an OR-like separator (as opposed to the AND-like
} ";&" separator)
This analogy doesn't work. Semantically, the test for whether $mycase
matches any one of the labels occurs once at the top of the statement.
Control then jumps into the body as if with a GOTO, and thereafter all
you're able to change with ;& is how early you exit from the body. It
isn't anything like AND / OR.
By comparison, your proposed ;| requires the interpreter to reproduce
the pattern match test at every label, which implies storing the result
of expanding $mycase, etc. Most languages don't allow one to hide quite
that much complexity behind syntactic sugar.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Case statement with ";|" [not implemented]
2007-01-19 4:52 ` Bart Schaefer
@ 2007-01-19 12:01 ` Peter Stephenson
0 siblings, 0 replies; 3+ messages in thread
From: Peter Stephenson @ 2007-01-19 12:01 UTC (permalink / raw)
To: zsh-users
Bart Schaefer wrote:
> } Note that ";|" provides an OR-like separator (as opposed to the AND-like
> } ";&" separator)
>
> This analogy doesn't work. Semantically, the test for whether $mycase
> matches any one of the labels occurs once at the top of the statement.
> Control then jumps into the body as if with a GOTO, and thereafter all
> you're able to change with ;& is how early you exit from the body. It
> isn't anything like AND / OR.
>
> By comparison, your proposed ;| requires the interpreter to reproduce
> the pattern match test at every label, which implies storing the result
> of expanding $mycase, etc. Most languages don't allow one to hide quite
> that much complexity behind syntactic sugar.
I think we simply have to apply the restriction that the word in the
case statement is expanded only once at the start of the case statement.
I don't see that's either unnatural or confusing. With this it looks
like it ought to be quite straightforward, possible even trivial, to
implement.
--
Peter Stephenson <pws@csr.com> Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK Tel: +44 (0)1223 692070
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2007-01-18 19:53 Case statement with ";|" [not implemented] Gerald Lai
2007-01-19 4:52 ` Bart Schaefer
2007-01-19 12:01 ` Peter Stephenson
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