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Merge pull request #4514 from sternenseemann/tryeval-doc

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Include note about type of catched errors in tryEval documentation
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Eelco Dolstra 2021-02-03 18:20:24 +01:00 committed by GitHub
parent 0e05cb6c61 76d8bdfe35
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12
src/libexpr/primops.cc
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@ -696,10 +696,14 @@ static RegisterPrimOp primop_tryEval({
Try to shallowly evaluate *e*. Return a set containing the
attributes `success` (`true` if *e* evaluated successfully,
`false` if an error was thrown) and `value`, equalling *e* if
successful and `false` otherwise. Note that this doesn't evaluate
*e* deeply, so ` let e = { x = throw ""; }; in (builtins.tryEval
e).success ` will be `true`. Using ` builtins.deepSeq ` one can
get the expected result: `let e = { x = throw ""; }; in
successful and `false` otherwise. `tryEval` will only prevent
errors created by `throw` or `assert` from being thrown.
Errors `tryEval` will not catch are for example those created
by `abort` and type errors generated by builtins. Also note that
this doesn't evaluate *e* deeply, so `let e = { x = throw ""; };
in (builtins.tryEval e).success` will be `true`. Using
`builtins.deepSeq` one can get the expected result:
`let e = { x = throw ""; }; in
(builtins.tryEval (builtins.deepSeq e e)).success` will be
`false`.
)",