[Nix-dev] Re: Proposal: tryCatch function

[Michael Raskin]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Eelco Dolstra wrote:
> You could throw a value, and rethrow it if you can't handle it.  However, having
> distinct kinds of exceptions is a problem in a purely functional language, since
> the exception that gets thrown might depend on the evaluation order.  This is
> why Haskell only allows exceptions to be caught in the I/O monad.

Even just getting the message thrown is already enough. On the other
hand, if the only allowed use is beautifying and rethrowing, we get more
or less current behavior - you cannot tell which of the errors will show
up first, but you do not risk getting the same expression to produce
different derivations for the reasons not described in language definition.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iQEcBAEBAgAGBQJJYx6MAAoJEE6tnN0aWvw3rk8IAInCcf1dHFDo2k8hQRZxZalu
K6bALIxQCnEdce3G3GOC2TlkKD+rux+eHGPFOYZDLNLAP3mCmR10ymdXVJKKzrEO
hbKGqCHPSnRSROh5Dv0XK+BMVZhj7fZIGtccfg9T2OwrXEHkiWnjfD3AprJtzQCw
eX5ONFaCLFWiOATXBHvnfFZ5GMABYaQruA7rEHN05xPyUyrD74Pktve/vvVFlj+2
AcjWthu6ckx4vspdtRKO9H5yBN7YB74GiuR0L/My69bawR4gGuWzzlAITTOq/iM0
sQUeshROMSzXd+WMZl4z4vBs6rPz5O+cJexdiq2Qw7nTUHTWF8EkqSaA9z6vw+M=
=0Bbn
-----END PGP SIGNATURE-----