From 7c9ad4d0d7bbd3896c99fa0b252d21a69e18b711 Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <infinisil@icloud.com>
Date: Tue, 3 Sep 2019 07:32:44 +0200
Subject: docs: Note that tryEval doesn't do deep evaluation

(cherry picked from commit e4ea3e03066a760c8cd462108af99aebaaa44c1b)
---
 doc/manual/expressions/builtins.xml | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

(limited to 'doc/manual/expressions/builtins.xml')

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>
-- 
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