builtins.tryEval

Takes 1 arguments

e

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. tryEval only prevents errors created by throw or assert from being thrown. Errors tryEval doesn't 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 is true. Using builtins.deepSeq one can get the expected result: let e = { x = throw ""; }; in (builtins.tryEval (builtins.deepSeq e e)).success is false.

tryEval intentionally does not return the error message, because that risks bringing non-determinism into the evaluation result, and it would become very difficult to improve error reporting without breaking existing expressions. Instead, use builtins.addErrorContext to add context to the error message, and use a Nix unit testing tool for testing.

Noogle detected

tryEval :: a