Re: RC_EXPAND_PARAM bug

["Bart Schaefer" <schaefer@xxxxxxxxxxxxxxxx>]

On Jul 30,  1:16am, Zoltan Hidvegi wrote:
} Subject: Re: RC_EXPAND_PARAM bug
}
} > I'm still not comprehending this.
} 
} OK, I tell you what subst.c does.

Thank you!

} prefix${^a}suffix
} 
} Suppose that prefix does not have anything to expand.  paramsubst is
} called to expand this string, which expands ${^a}.  There are three
} cases:
} 
} 1. `a' was an empty array.  In that case the expansion is the empty list,
}    and suffix is not evaluated (so even if there is a $[i++] in suffix, i
}    will not change).

Hrm.  I think I would have expected to get prefixsuffix, with suffix
evaluated.  That's what you get when a=("") or a="", but I can't decide
if that represents an argument in favor, or against.

} 3. `a' has more than one elements.  In that case stringsubst is called
}    for suffix alone (which may call paramsubst again to expand something
}    in suffix), and the result will be be a list.  This list is combined
}    with the expansion of ${^a}.  If suffix expands to an empty list, the
}    result will be empty

Again I find the empty list behavior unexpected, but possibly defensible.

} This guarantees left to right evaluation, everything is evaluated at most
} once,

These are both good things.

} and everything is evaluated once unless there is an rc-expansion of
} an empty array which discards everything following that array.

It's that one that gives me pause.

} What would be the preferred evaluation of ${^a}1${^^x}?

What does the real "rc" shell do?  Duplicating it would be my first choice,
unless it does something wildly different than any previous version of zsh.

} Alternatives:
} 
} 1. a1x ay b1x by  (current)
} 
} 2. a1x y b1x y    (beta16 and older)
} 
} 3. a1x b1x y      (just an other logical solution).

The important question for me is, where are the word breaks in (2)?
That is, if I do:

  z=(${^a}1${^^x})

What is ${#z}?  If z is ("a1x y" "b1x y"), then I think that's wrong.
I presume you mean 4 words, though, in which case I think it's right,
in spite of what I just told Geoff. :-}

On Jul 30,  9:46am, Andrej Borsenkow wrote:
} Subject: Re: RC_EXPAND_PARAM bug
}
} zsh-3.1.2 with RC_EXPAND_PARAM bugfix.
} 
} % echo ${^a}1${^^x}
} a1x ay b1x by
} 
} % echo ${^^a}1${^x}
} a b1x b1y
} 
} It looks illogical. Either the latter should be 'ax b1x ay b1y' or the
} former 'a1x b1x y'. 

I agree with Andrej on that.  If you're going to map over lists, you
have to map over them in the prefix too, not just in the suffix.

However, I don't like the behavior of (3), i.e. that when ${x} is a list
then the word break interrupts the rc-expansion.  I'd prefer that the
expansion proceed across the suffix in the same way regardless of whether
x is an array or a string, and then introduce the word breaks at the end.
That's why I prefer (2) -- but I'd still like to know how "rc" does it.

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com