lix/doc/manual/rl-next/better-errors-in-nix-repl.md
Rebecca Turner 1e017e2763
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2024-03-29 22:57:40 -07:00

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---
synopsis: Concise error printing in `nix repl`
prs: 9928
---
Previously, if an element of a list or attribute set threw an error while
evaluating, `nix repl` would print the entire error (including source location
information) inline. This output was clumsy and difficult to parse:
```
nix-repl> { err = builtins.throw "uh oh!"; }
{ err = «error:
… while calling the 'throw' builtin
at «string»:1:9:
1| { err = builtins.throw "uh oh!"; }
| ^
error: uh oh!»; }
```
Now, only the error message is displayed, making the output much more readable.
```
nix-repl> { err = builtins.throw "uh oh!"; }
{ err = «error: uh oh!»; }
```
However, if the whole expression being evaluated throws an error, source
locations and (if applicable) a stack trace are printed, just like you'd expect:
```
nix-repl> builtins.throw "uh oh!"
error:
… while calling the 'throw' builtin
at «string»:1:1:
1| builtins.throw "uh oh!"
| ^
error: uh oh!
```