In reply to @cdepillabout:matrix.org
GHCs are available as haskell.compiler.ghc910*, and the package sets at haskell.packages.ghc910*.lens (or whatever). Although keep in mind that sometimes things don't work with the non-default compiler.

In reply to @setunset:matrix.org
Thanks. But how large is th delta ?How many versions I can expect to be available when they are not yet released to the unstable branch?

In reply to @alexfmpe:matrix.org
also, while the compiler is cached, the package set itself isn't, so the first build will be annoying

I am getting these compiler errors on aarch64-darwin after upgrading to ghc 9.8.4

       > /private/tmp/nix-build-my-package-0.0.0.drv-2/ghc39648_0/ghc_2167.s:8135994:2: error:
       >      error: fixup value out of range
       >             cbnz x17, Lc3HV0l
       >             ^
       >         |
       > 8135994 |         cbnz x17, Lc3HV0l
       >         |  ^
       >
       > /private/tmp/nix-build-my-package-0.0.0.drv-2/ghc39648_0/ghc_2167.s:8136336:2: error:
       >      error: fixup value out of range
       >             b.hi Lc3HV1y
       >             ^
       >         |
       > 8136336 |         b.hi Lc3HV1y
       >         |  ^
       >
       > <no location info>: error:
       >     `cc' failed in phase `Assembler'. (Exit code: 1)

It compiles on x86-linux. Anyone seen this before?

maralorn Okay, so be it

{
  inputs = {
    nixpkgs.url = "https://github.com/NixOS/nixpkgs/archive/08f2208.tar.gz";
    flake-utils.url = "github:numtide/flake-utils";
    haskell-updates.url = "github:NixOS/nixpkgs/haskell-updates";
  };
  outputs = { self, nixpkgs, haskell-updates, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
            inherit system;
            overlays = [
                (final: prev: {
                    haskell-language-server =
                        haskell-updates.legacyPackages.${system}.haskellPackages.haskell-language-server;
                })
            ];
        };
      in
      {
        devShell = pkgs.mkShell {
          buildInputs = with pkgs; [
            stack
            haskell.compiler.ghc9102
            (haskell-language-server.override { supportedGhcVersions = [ "9102" ];})
            haskellPackages.fourmolu
            haskellPackages.hoogle
            zlib
          ];
          NIX_LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [
            pkgs.stdenv.cc.cc
            pkgs.openssl
            pkgs.zlib
          ];
          NIX_LD = pkgs.lib.fileContents "${pkgs.stdenv.cc}/nix-support/dynamic-linker";
        };
      }
    );
}

>   error: function 'anonymous lambda' called with unexpected argument 'supportedGhcVersions'

maralorn Okay, so be it

{
  inputs = {
    nixpkgs.url = "https://github.com/NixOS/nixpkgs/archive/08f2208.tar.gz";
    flake-utils.url = "github:numtide/flake-utils";
    haskell-updates.url = "github:NixOS/nixpkgs/haskell-updates";
  };
  outputs = { self, nixpkgs, haskell-updates, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
            inherit system;
            overlays = [
                (final: prev: {
                    haskell-language-server =
                        haskell-updates.legacyPackages.${system}.haskellPackages.haskell-language-server;
                })
            ];
        };
      in
      {
        devShell = pkgs.mkShell {
          buildInputs = with pkgs; [
            stack
            haskell.compiler.ghc9102
            (haskell-language-server.override { supportedGhcVersions = [ "9102" ];})
            haskellPackages.fourmolu
            haskellPackages.hoogle
            zlib
          ];
          NIX_LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [
            pkgs.stdenv.cc.cc
            pkgs.openssl
            pkgs.zlib
          ];
          NIX_LD = pkgs.lib.fileContents "${pkgs.stdenv.cc}/nix-support/dynamic-linker";
        };
      }
    );
}

error: function 'anonymous lambda' called with unexpected argument 'supportedGhcVersions'

In reply to @setunset:matrix.org

maralorn Okay, so be it

{
  inputs = {
    nixpkgs.url = "https://github.com/NixOS/nixpkgs/archive/08f2208.tar.gz";
    flake-utils.url = "github:numtide/flake-utils";
    haskell-updates.url = "github:NixOS/nixpkgs/haskell-updates";
  };
  outputs = { self, nixpkgs, haskell-updates, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
            inherit system;
            overlays = [
                (final: prev: {
                    haskell-language-server =
                        haskell-updates.legacyPackages.${system}.haskellPackages.haskell-language-server;
                })
            ];
        };
      in
      {
        devShell = pkgs.mkShell {
          buildInputs = with pkgs; [
            stack
            haskell.compiler.ghc9102
            (haskell-language-server.override { supportedGhcVersions = [ "9102" ];})
            haskellPackages.fourmolu
            haskellPackages.hoogle
            zlib
          ];
          NIX_LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [
            pkgs.stdenv.cc.cc
            pkgs.openssl
            pkgs.zlib
          ];
          NIX_LD = pkgs.lib.fileContents "${pkgs.stdenv.cc}/nix-support/dynamic-linker";
        };
      }
    );
}

>   error: function 'anonymous lambda' called with unexpected argument 'supportedGhcVersions'

You should use haskell-language-server from a different haskellPackages

Instead of using top-level haskell-language-server, consider haskell.packages.ghc9102.haskell-language-server

haskellPackages.fourmolu

BTW, fourmolu will not work with a new syntax too