Re: let and for vs. lambda variations

[hanche@ams.sunysb.edu (Harald Hanche-Olsen)]

Actually, even the multiple binding forms can be rewritten as lambdas,
using the wrapping trick, but it would be awkward and require some
obfuscated code:

  let (x=a b;y=c d) cmd  -->

  @ xy {@ y {@ x {cmd} <=$xy(1)} $xy(2)} <={wrap a b} <={wrap c d}

where `xy' is a symbol that does not appear in the text of cmd.  (!)

I hadn't realized before that local can be rewritten as a lambda, but
after a little though I came up with the following, for a single
binding local (so the above obfuscation is avoided):

  local (x=a b) cmd  -->  %local x <={wrap a b} cmd

where 

  fn %local var wrapped-list cmd {
    let (old=$$var)
      unwind-protect {
        $var = <={$wrapped-list}
        $cmd
      }{$var = $old}}

(Whose let is of course rewritable as a lambda...)  Funny, I don't
even see a problem with name space collisions!

If you insist that for, local, and let stay together or leave
together, I think I'll vote that they stay.  The obfuscation needed
for handling the multiple binding let without making it a let* is just
too much.

But who uses multiple binding for, anyway?  And for what?

- Harald