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docs: make sample code valid Nix expressions #354606

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Nov 8, 2024
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docs: make sample code valid Nix expressions #354606

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24 changes: 18 additions & 6 deletions lib/fixed-points.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -160,15 +160,19 @@ rec {
A fixed-point function returning an attribute set has the form

```nix
final: { # attributes }
final: {
# attributes
}
```

where `final` refers to the lazily evaluated attribute set returned by the fixed-point function.

An overlay to such a fixed-point function has the form

```nix
final: prev: { # attributes }
final: prev: {
# attributes
}
```

where `prev` refers to the result of the original function to `final`, and `final` is the result of the composition of the overlay and the original function.
Expand All @@ -177,17 +181,25 @@ rec {

```nix
let
f = final: { # attributes };
overlay = final: prev: { # attributes };
f = final: {
# attributes
};
overlay = final: prev: {
# attributes
};
in extends overlay f;
```

To get the value of `final`, use `lib.fix`:

```nix
let
f = final: { # attributes };
overlay = final: prev: { # attributes };
f = final: {
# attributes
};
overlay = final: prev: {
# attributes
};
g = extends overlay f;
in fix g
```
Expand Down