[Nix-dev] Re: Proposal: tryCatch function

[Michael Raskin]

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Eelco Dolstra wrote:
>>> What should
>>> (throw "foo") + (throw "bar")
>>> return?
>> Usually, you start reading a string by the left-hand side, therefore,
>> I would say: throw "foo".
> 
> Which was exactly what I meant with evaluation order :-)  The language semantics
> don't specify in what order arguments are evaluated, so it might also be `throw
> "bar"'.
> 
> Of course we could say that useful error messages are more important than a
> "clean" semantics, but it's still a concern.

We already do not have total cleanness for expressions containing
errors. So tryRethrow will leave us better off. On the other hand, I
agree with you that clean semantics for the cases where derivation is
successfully produced is more important than anything because it is a
part of the perceived goal of Nix.
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