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| author | Silvan Mosberger <infinisil@icloud.com> | 2019-09-03T05·32+0200 |
|---|---|---|
| committer | Eelco Dolstra <edolstra@gmail.com> | 2019-10-09T14·25+0200 |
| commit | 7c9ad4d0d7bbd3896c99fa0b252d21a69e18b711 (patch) | |
| tree | c68fa88cfc3dfde0ed0859a4ba68a8755d880272 /doc/manual | |
| parent | fa028194e9e707e7aa35990e074f5c6672b50f98 (diff) | |
docs: Note that tryEval doesn't do deep evaluation
(cherry picked from commit e4ea3e03066a760c8cd462108af99aebaaa44c1b)
Diffstat (limited to 'doc/manual')
| -rw-r--r-- | doc/manual/expressions/builtins.xml | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/doc/manual/expressions/builtins.xml b/doc/manual/expressions/builtins.xml index ffede99c5841..465fa1e0b001 100644 --- a/doc/manual/expressions/builtins.xml +++ b/doc/manual/expressions/builtins.xml @@ -1605,12 +1605,18 @@ stdenv.mkDerivation (rec { <term><function>builtins.tryEval</function> <replaceable>e</replaceable></term> - <listitem><para>Try to evaluate <replaceable>e</replaceable>. + <listitem><para>Try to shallowly evaluate <replaceable>e</replaceable>. Return a set containing the attributes <literal>success</literal> (<literal>true</literal> if <replaceable>e</replaceable> evaluated successfully, <literal>false</literal> if an error was thrown) and <literal>value</literal>, equalling <replaceable>e</replaceable> - if successful and <literal>false</literal> otherwise. + if successful and <literal>false</literal> otherwise. Note that this + doesn't evaluate <replaceable>e</replaceable> deeply, so + <literal>let e = { x = throw ""; }; in (builtins.tryEval e).success + </literal> will be <literal>true</literal>. Using <literal>builtins.deepSeq + </literal> one can get the expected result: <literal>let e = { x = throw ""; + }; in (builtins.tryEval (builtins.deepSeq e e)).success</literal> will be + <literal>false</literal>. </para></listitem> </varlistentry> |