[Nix-dev] Re: Proposal: tryCatch function

[Andres Loeh]

Mainly because of the already mentioned trickyness that exceptions in
lazy languages tend to escape their surrounding try-block, try-catch
is generally considered not a very useful construct in the face of laziness.

The escaping should not only be a problem for functions, but also for
any form of compound lazy data (i.e., attribute sets in the Nix language).

<religion>Exceptions in a pure language are evil and should be avoided,
not encouraged.</religion>

Regarding evaluation order (left-to-right or right-to-left or unspecified):
I doubt that Nix currently uses a nondeterministic strategy, so I
don't think it's a big problem in fixing that particular subproblem by
adopting left-to-right.

Cheers,
  Andres