| 20 Mar 2026 |
 piegames | I have a hunch this might be a callsite problem | 23:30:14 |
| piegames | In reply to @blokyk:matrix.org
me too, but i don't know how the evaluator actually works internally, and i saw that trace has a forceValue(args[1]), and i know for a fact that trace doesn't have that bug, so i figured it'd fix it I mean you can just try it out and see if it helps | 23:30:42 |
 zoë (she/her) | nix-repl> builtins.mapAttrs (n: v: v) (break { a = 5; })
error:
… while calling the 'mapAttrs' builtin
at «string»:1:1:
1| builtins.mapAttrs (n: v: v) (break { a = 5; })
| ^
… while evaluating the second argument passed to builtins.mapAttrs
error: expected a set but found a thunk: «thunk»
| 23:31:43 |
| zoë (she/her) | yep that's what i did and it seems to work how i'd expect (i.e. the above expression evaluates fine) | 23:32:40 |
| piegames | And if you replace break with identity or with trace it works? | 23:32:56 |
| zoë (she/her) | it seems to be the case with most of the builtins i've tried, from memory | 23:33:13 |
| zoë (she/her) | yep | 23:33:18 |
| zoë (she/her) | nix-repl> builtins.mapAttrs (n: v: v) (builtins.trace "hi" { a = 5; })
trace: hi
{ a = 5; }
| 23:33:40 |
| zoë (she/her) | * it seems to be the case with most of the builtins i've tried, from memory, which is why i starting looking at prim_break first | 23:34:13 |
| zoë (she/her) | to me the most dangerous part is this, cause it's a lot more silent:
nix-repl> builtins.isAttrs (builtins.trace "hi" { a = 5; })
trace: hi
true
nix-repl> builtins.isAttrs (break { a = 5; })
false
| 23:35:15 |
| zoë (she/her) | another fun one is this :D
nix-repl> builtins.map (x: x) (break [])
[ ]
nix-repl> builtins.map (x: x) (break [ 5 ])
error:
… while calling the 'map' builtin
at «string»:1:1:
1| builtins.map (x: x) (break [ 5 ])
| ^
… while evaluating the second argument passed to builtins.map
error: expected a list but found a thunk: «thunk»
| 23:36:31 |
| piegames | Yeah okay | 23:37:17 |
| piegames | Can you please open an issue with all of this? | 23:37:28 |
| zoë (she/her) | sure | 23:37:39 |
| piegames | But also you are right that a forceValue is missing in the primop | 23:37:42 |
| zoë (she/her) | i wasn't sure how widely known this was, since i encountered it all the time (on both cppnix and lix) | 23:38:29 |
| piegames | The reason being, that there is some undocumented invariant spread across the evaluator as to when a value is alloeed to be thunked. And break currently violates that, which is why forceValue on a break does not the right thing | 23:38:54 |
| piegames | In reply to @blokyk:matrix.org
i wasn't sure how widely known this was, since i encountered it all the time (on both cppnix and lix) I think you may be the single most active user of the debug REPL, maybe ever | 23:39:41 |
| zoë (she/her) | xD | 23:39:50 |
| zoë (she/her) | i don't even use it that much ;-; it does pain me how unknown and somewhat uncared-for it is ;-; | 23:40:21 |
| zoë (she/her) | * i don't even use it that much ;-; it does pain me how unknown and somewhat uncared-for it is ._. | 23:40:24 |
| piegames | To be frank it shouldn't exist in its current form in the first place | 23:40:59 |
| piegames | It is uncared for because touching it is exceptionally unforgiving, and it is unknown because nobody bothered documenting a hacky half-working feature | 23:42:26 |
| zoë (she/her) | done! would you want me to make a CL for this that simply adds forceValue (+changes the tests)? | 23:57:50 |
| 21 Mar 2026 |
| zoë (she/her) | * done! would you want me to make a CL for this that simply adds forceValue (+changes the tests)? | 00:00:45 |
| zoë (she/her) | * done! so would a CL for this that simply adds forceValue (+changes the tests) be ok? | 00:01:04 |
 emily | that's not valid in all the cases multiline strings are | 03:17:48 |
| emily | hmm, or maybe it is? I guess attrset keys can't use it. but, uh, flake inputs? | 03:18:22 |
| emily | I think an interpolated subexpression has a very different characteristic to an escape in a string literal though | 03:19:00 |
|  adobo joined the room. | 10:58:40 |
