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Assertion failure in eval.cc with partial application #1102

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opened 2026-01-14 19:09:15 +00:00 by lunagl · 4 comments

lunagl commented

2026-01-14 19:09:15 +00:00

Describe the bug

apply = f: arg: f arg;
applyList = builtins.foldl' apply;

applyList lib.nameValuePair ["a" "b"]; # this works
x = applyList lib.nameValuePair;
x ["a" "b"] # this fails

The last expression causes Lix to abort with this message:

nix: lix/libexpr/eval.cc:1717: void nix::EvalState::callFunction(Value &, std::span<Value>, Value &, const PosIdx): Assertion `!vCur.app().left().isApp()' failed.

The code evaluates correctly when changing the definition of applyList to

applyList = f: builtins.foldl' apply f;

`nix --version` output

nix (Lix, like Nix) 2.94.0

## Describe the bug ```nix apply = f: arg: f arg; applyList = builtins.foldl' apply; applyList lib.nameValuePair ["a" "b"]; # this works x = applyList lib.nameValuePair; x ["a" "b"] # this fails ``` The last expression causes Lix to abort with this message: ``` nix: lix/libexpr/eval.cc:1717: void nix::EvalState::callFunction(Value &, std::span<Value>, Value &, const PosIdx): Assertion `!vCur.app().left().isApp()' failed. ``` The code evaluates correctly when changing the definition of `applyList` to ```nix applyList = f: builtins.foldl' apply f; ``` ## `nix --version` output `nix (Lix, like Nix) 2.94.0`

lunagl added the

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2026-01-14 19:09:15 +00:00

raito added this to the 2.94.1 milestone

2026-01-14 19:16:28 +00:00

raito commented

2026-01-14 21:26:48 +00:00

Owner

Thank you @lunagl for the bug report. We are working on a fix. Did you encounter this in production code or is this a case that stumbled on while writing your own code?

lix-bot commented

2026-01-14 21:59:12 +00:00

Member

This issue was mentioned on Gerrit on the following CLs:

commit message in cl/4942 ("libexpr: fix app chain extension")
commit message in cl/4943 ("libexpr: fix app chain extension")

This issue was mentioned on Gerrit on the following CLs: * commit message in [cl/4942](https://gerrit.lix.systems/c/lix/+/4942) ("libexpr: fix app chain extension") * commit message in [cl/4943](https://gerrit.lix.systems/c/lix/+/4943) ("libexpr: fix app chain extension")

lix-project referenced this issue from a commit

2026-01-14 22:20:32 +00:00

libexpr: fix app chain extension

lix-project closed this issue

2026-01-14 22:20:32 +00:00

lix-project referenced this issue from a commit

2026-01-14 23:27:59 +00:00

libexpr: fix app chain extension

lunagl commented

2026-01-15 00:21:06 +00:00

Author

@raito wrote in #1102 (comment):

Thank you @lunagl for the bug report. We are working on a fix. Did you encounter this in production code or is this a case that stumbled on while writing your own code?

Thank you for fixing this so quickly! I encountered it when writing my own code, I don't know of any public projects that run into this issue

@raito wrote in https://git.lix.systems/lix-project/lix/issues/1102#issuecomment-17201: > Thank you @lunagl for the bug report. We are working on a fix. Did you encounter this in production code or is this a case that stumbled on while writing your own code? Thank you for fixing this so quickly! I encountered it when writing my own code, I don't know of any public projects that run into this issue

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raito commented

2026-01-15 00:25:40 +00:00

Owner

Awesome, thank you so much for the report! We are planning to release 2.94.1 in response to this issue on an accelerated schedule.

❤️ 1