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doc/haskell: Add clarifications in section about versions

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maralorn 2023-02-17 16:50:47 +01:00 committed by sternenseemann
parent 571a705593
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1 changed files with 13 additions and 6 deletions
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doc/languages-frameworks/haskell.section.md
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@ -137,7 +137,12 @@ set the default version to a version older than the newest on Hackage. We do
this to get them or their reverse dependencies to compile in our package set.
4. For all packages, for which the newest Hackage version is not the default
version, there will also be a `haskellPackages.foo_x_y_z` package with the
newest version.
newest version. The `x_y_z` part encodes the version with dots replaced by
underscores. When the newest version changes by a new release to Hackage the
old package will disappear under that name and be replaced by a newer one under
the name with the new version. The package name including the version will
also disappear when the default version e.g. from Stackage catches up with the
newest version from Hackage.
5. For some packages, we also manually add other `haskellPackages.foo_x_y_z`
versions, if they are required for a certain build.
@ -161,12 +166,14 @@ given in the `.cabal` file of your package and all its dependencies.
The [Haskell builder in nixpkgs](#haskell-mkderivation) does no such thing.
It will simply take as input packages with names off the desired dependencies
and just check whether they fulfill the version bounds and (by default, see
`jailbreak`) fail if they don’t.
and just check whether they fulfill the version bounds and fail if they don’t
(by default, see `jailbreak` to circumvent this).
The package resolution is done by the `haskellPackages.callPackage` function
which will, e.g., use `haskellPackages.aeson` for a package input of name
`aeson`.
The `haskellPackages.callPackage` function does the package resolution.
It will, e.g., use `haskellPackages.aeson`which has the default version as
described above for a package input of name `aeson`. (More general:
`<packages>.callPackage f` will call `f` with named inputs provided from the
package set `<packages>`.)
While this is the default behavior, it is possible to override the dependencies
for a specific package, see
[`override` and `overrideScope`](#haskell-overriding-haskell-packages).