diff options
| author | sterni <sternenseemann@systemli.org> | 2022-10-15T13·52+0200 |
|---|---|---|
| committer | clbot <clbot@tvl.fyi> | 2022-10-15T14·12+0000 |
| commit | f3c27f1717f0b92b05340c0bc6ba44007ce9d90b (patch) | |
| tree | 989566dc26387d1e7849df4de0bdc841cdf963aa /tvix/eval/docs | |
| parent | caf9cbf71147054c01c6fdf49773d646cbfb46eb (diff) | |
fix(tvix/eval): bring foldl' strictness in line with C++ Nix r/5133
Working on https://github.com/NixOS/nix/pull/7158, I discovered that C++ Nix actually is strict in the accumulator, just not in the first value. This seems due to the fact that in the C++ evaluator, function calls don't seem to be thunked unconditionally and foldl' just elects not to wrap it in a thunk (don't quote me on this summary, even though it seems to line up with the code for primop_foldlStrict and testable behavior). It doesn't seem worth it to risk breaking the odd Nix expression just to be strict in one more value per invocation of foldl' (i.e. the initial accumulator value `nul`), so let's match the existing C++ Nix behavior here. Change-Id: If59e62271a90d97cb440f0ca72a58ec7840d1690 Reviewed-on: https://cl.tvl.fyi/c/depot/+/7022 Autosubmit: sterni <sternenseemann@systemli.org> Tested-by: BuildkiteCI Reviewed-by: tazjin <tazjin@tvl.su>
Diffstat (limited to 'tvix/eval/docs')
| -rw-r--r-- | tvix/eval/docs/language-issues.md | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/tvix/eval/docs/language-issues.md b/tvix/eval/docs/language-issues.md index fb74b1d3d324..26401665bbb5 100644 --- a/tvix/eval/docs/language-issues.md +++ b/tvix/eval/docs/language-issues.md @@ -17,7 +17,6 @@ maybe to get rid of the behavior in all implementations for good. Below is an * [Behaviour of nested attribute sets depends on definition order][i7111] * [Partially constructed attribute sets are observable during dynamic attr names construction][i7012] * [Nix parsers merges multiple attribute set literals for the same key incorrectly depending on definition order](i7115) -* [builtins.foldl' doesn't seem to be strict](p7158) On the other hand, there is behavior that seems to violate one's expectation about the language at first, but has good enough reasons from an implementor's @@ -35,6 +34,12 @@ perspective to keep them: implementation already merges at parse time, making nested attribute keys syntactic sugar effectively. +Other behavior is just odd, surprising or underdocumented: + +* `builtins.foldl'` doesn't force the initial accumulator (but all other + intermediate accumulator values), differing from e.g. Haskell, see + the [relevant PR discussion](p7158). + [i7111]: https://github.com/NixOS/nix/issues/7111 [i7012]: https://github.com/NixOS/nix/issues/7012 [i7115]: https://github.com/NixOS/nix/issues/7115 |