try to permit building with GHC 9.6

flake.nix

@@ -4,13 +4,49 @@
     flake-parts.url = "github:hercules-ci/flake-parts";
     haskell-flake.url = "github:srid/haskell-flake";
   };
-  outputs = inputs@{ self, nixpkgs, flake-parts, ... }:
-    flake-parts.lib.mkFlake { inherit inputs; } {
-      systems = nixpkgs.lib.systems.flakeExposed;
+  outputs = inputs:
+  inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = inputs.nixpkgs.lib.systems.flakeExposed;
       imports = [ inputs.haskell-flake.flakeModule ];
       perSystem = { self', pkgs, config, ... }: {
-        packages.default = self'.packages.fortran-src;
-        haskellProjects.default = {};
+        packages.default  = self'.packages.fortran-src-ghc92-fortran-src;
+        devShells.default = self'.devShells.fortran-src-ghc92;
+
+        haskellProjects.ghc92 = import ./haskell-flake-ghc92.nix pkgs;
+        haskellProjects.fortran-src-ghc92 = {
+          basePackages = config.haskellProjects.ghc92.outputs.finalPackages;
+          devShell = {
+            tools = hp: {
+              # use nixpkgs cabal-install
+              cabal-install = pkgs.cabal-install;
+
+              # disable these while unused (often slow/annoying to build)
+              haskell-language-server = null;
+              ghcid = null;
+              hlint = null;
+            };
+          };
+        };
+
+        haskellProjects.ghc94 = import ./haskell-flake-ghc94.nix pkgs;
+        haskellProjects.fortran-src-ghc94 = {
+          basePackages = config.haskellProjects.ghc94.outputs.finalPackages;
+          devShell = {
+            tools = hp: {
+              # use nixpkgs cabal-install
+              cabal-install = pkgs.cabal-install;
+
+              # disable these while unused (often slow/annoying to build)
+              haskell-language-server = null;
+              ghcid = null;
+              hlint = null;
+            };
+          };
+        };
+
+        haskellProjects.ghc96 = {
+          basePackages = pkgs.haskell.packages.ghc96;
+        };
       };
     };
 }

fortran-src.cabal

@@ -1,6 +1,6 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.37.0.
+-- This file has been generated from package.yaml by hpack version 0.35.2.
 --
 -- see: https://github.com/sol/hpack
 
@@ -200,9 +200,9 @@ library
     , mtl >=2.2 && <3
     , pretty >=1.1 && <2
     , process >=1.2.0.0
-    , singletons >=3.0 && <3.2
-    , singletons-base >=3.0 && <3.2
-    , singletons-th >=3.0 && <3.2
+    , singletons ==3.0.*
+    , singletons-base >=3.0 && <3.3
+    , singletons-th >=3.0 && <3.3
     , temporary >=1.2 && <1.4
     , text >=1.2 && <2.1
     , uniplate >=1.6 && <2
@@ -264,9 +264,9 @@ executable fortran-src
     , mtl >=2.2 && <3
     , pretty >=1.1 && <2
     , process >=1.2.0.0
-    , singletons >=3.0 && <3.2
-    , singletons-base >=3.0 && <3.2
-    , singletons-th >=3.0 && <3.2
+    , singletons ==3.0.*
+    , singletons-base >=3.0 && <3.3
+    , singletons-th >=3.0 && <3.3
     , temporary >=1.2 && <1.4
     , text >=1.2 && <2.1
     , uniplate >=1.6 && <2
@@ -363,9 +363,9 @@ test-suite spec
     , mtl >=2.2 && <3
     , pretty >=1.1 && <2
     , process >=1.2.0.0
-    , singletons >=3.0 && <3.2
-    , singletons-base >=3.0 && <3.2
-    , singletons-th >=3.0 && <3.2
+    , singletons ==3.0.*
+    , singletons-base >=3.0 && <3.3
+    , singletons-th >=3.0 && <3.3
     , temporary >=1.2 && <1.4
     , text >=1.2 && <2.1
     , uniplate >=1.6 && <2

haskell-flake-ghc92.nix

@@ -0,0 +1,30 @@
+pkgs: {
+  # disable local project options (always do this for package sets)
+  defaults.packages = {};
+  devShell.enable = false;
+  autoWire = [];
+
+  basePackages = pkgs.haskell.packages.ghc92;
+  packages = {
+    # GHC 9.2 libraries
+    singletons-th.source   = "3.1";
+    singletons-base.source = "3.1";
+    singletons.source = "3.0.1"; # req because singletons-th-3.1 had bad bounds
+    th-desugar.source = "1.13.1";
+    th-abstraction.source = "0.4.5.0";
+  };
+
+  # (note this is actually unused/we have to duplicate because it doesn't get
+  # packed into basePackages or any key we can use... but nice to document here)
+  devShell = {
+    tools = hp: {
+      # by default, haskell-flake uses the Haskell packages versions of these
+      # tools (from hp). be warned, these can be a pain to build alternatively,
+      # you may use nixpkgs versions via pkgs
+
+      # as of 2024-09-13 nixpkgs-unstable can't build cabal-install on GHC 9.2.
+      # no problem, use nixpkgs version (shouldn't really matter how built)
+      cabal-install = pkgs.cabal-install;
+    };
+  };
+}

haskell-flake-ghc94.nix

@@ -0,0 +1,30 @@
+pkgs: {
+  # disable local project options (always do this for package sets)
+  defaults.packages = {};
+  devShell.enable = false;
+  autoWire = [];
+
+  basePackages = pkgs.haskell.packages.ghc94;
+  packages = {
+    # GHC 9.4 libraries
+    singletons-th.source   = "3.1.1";
+    singletons-base.source = "3.1.1";
+    #singletons.source = "3.0.1";
+    th-desugar.source = "1.14";
+    th-abstraction.source = "0.4.5.0";
+  };
+
+  # (note this is actually unused/we have to duplicate because it doesn't get
+  # packed into basePackages or any key we can use... but nice to document here)
+  devShell = {
+    tools = hp: {
+      # by default, haskell-flake uses the Haskell packages versions of these
+      # tools (from hp). be warned, these can be a pain to build alternatively,
+      # you may use nixpkgs versions via pkgs
+
+      # as of 2024-09-13 nixpkgs-unstable can't build cabal-install on GHC 9.4.
+      # no problem, use nixpkgs version (shouldn't really matter how built)
+      cabal-install = pkgs.cabal-install;
+    };
+  };
+}

package.yaml

@@ -99,10 +99,11 @@ dependencies:
 - either ^>=5.0.1.1
 - process >= 1.2.0.0
 
-# 3.0 requires GHC 9.0; 3.1 requires GHC 9.2
-- singletons      >= 3.0 && < 3.2
-- singletons-th   >= 3.0 && < 3.2
-- singletons-base >= 3.0 && < 3.2
+- singletons      >= 3.0 && < 3.1
+
+# 3.0 = GHC 9.0, 3.1 = GHC 9.2, 3.1.1 = GHC 9.4, 3.2 = GHC 9.6
+- singletons-th   >= 3.0 && < 3.3
+- singletons-base >= 3.0 && < 3.3
 
 library:
   source-dirs: src