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Clarify how lazy evaluation helps to escape infinite co-recursion.

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In pill 13 `callPackage` and `pkgs` are defined co-recursively. The
author notes thas this is possible due to lazy evaluation, but for some
readers this may be confusing (as if lazy evaluation was some kind of
magic that makes infinite recursion not a problem).
This commit is contained in:
Ulya Trofimovich 2021-10-28 22:29:52 +01:00
parent b089684f6a
commit 36252cb882
1 changed files with 1 additions and 1 deletions
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pills/13-callpackage-design-pattern.xml
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@ -115,7 +115,7 @@
Note how easy is to override arguments in the case of <package>graphviz</package> without <package>gd</package>. But most importantly, how easy it was to merge two repositories: <literal>nixpkgs</literal> and our <literal>pkgs</literal>!
</para>
<para>
The reader should notice a magic thing happening. We're defining <literal>pkgs</literal> in terms of <literal>callPackage</literal>, and <literal>callPackage</literal> in terms of <literal>pkgs</literal>. That magic is possible thanks to lazy evaluation.
The reader should notice a magic thing happening. We're defining <literal>pkgs</literal> in terms of <literal>callPackage</literal>, and <literal>callPackage</literal> in terms of <literal>pkgs</literal>. That magic is possible thanks to lazy evaluation: <literal>builtins.intersectAttrs</literal> doesn't need to know the values in <literal>allPkgs</literal> in order to perform intersection, only the keys that do not require <literal>callPackage</literal> evaluation.
</para>
</section>
<section>