forked from lix-project/lix
19c5394971
The old way was not correct.
Here is an example:
```
$ nix-instantiate --eval --expr 'let x = a: throw "asdf"; in x 1' --show-trace
error: asdf
… while evaluating 'x'
at «string»:1:9:
1| let x = a: throw "asdf"; in x 1
| ^
… from call site
at «string»:1:29:
1| let x = a: throw "asdf"; in x 1
| ^
```
and yet also:
```
$ nix-instantiate --eval --expr 'let x = a: throw "asdf"; in x' --show-trace
<LAMBDA>
```
Here is the thing: in both cases we are evaluating `x`!
Nix is a higher-order languages, and functions are a sort of value. When
we write `x = a: ...`, `a: ...` is the expression that `x` is being
defined to be, and that is already a value. Therefore, we should *never*
get an trace that says "while evaluating `x`", because evaluating `a:
...` is *trival* and nothing happens during it!
What is actually happening here is we are applying `x` and evaluating
its *body* with arguments substituted for parameters. I think the
simplest way to say is just "while *calling* `x`", and so that is what I
changed it to.
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| .. | ||
| build-remote | ||
| libcmd | ||
| libexpr | ||
| libfetchers | ||
| libmain | ||
| libstore | ||
| libutil | ||
| nix | ||
| nix-build | ||
| nix-channel | ||
| nix-collect-garbage | ||
| nix-copy-closure | ||
| nix-env | ||
| nix-instantiate | ||
| nix-store | ||
| resolve-system-dependencies | ||
| toml11 | ||