chore: initial commit

lib/fp/default.nix

@@ -0,0 +1,36 @@
+{ core-inputs
+, user-inputs
+, snowfall-lib
+}:
+
+let
+  inherit (builtins) baseNameOf dirOf;
+  inherit (core-inputs.nixpkgs.lib) id foldr flip;
+in
+{
+  fp = rec {
+    # Compose two functions.
+    # Type: (b -> c) -> (a -> b) -> a -> c
+    # Usage: compose add-two add-one
+    #   result: (x: add-two (add-one x))
+    compose = f: g: x: f (g x);
+
+    # Compose many functions.
+    # Type: [(x -> y)] -> a -> b
+    # Usage: compose-all [ add-two add-one ]
+    #   result: (x: add-two (add-one x))
+    compose-all = foldr compose id;
+
+    # Call a function with an argument.
+    # Type: (a -> b) -> a -> b
+    # Usage: call (x: x + 1) 0
+    #   result: 1
+    call = f: x: f x;
+
+    # Apply an argument to a function.
+    # Type: a -> (a -> b) -> b
+    # Usage: call (x: x + 1) 0
+    #   result: 1
+    apply = flip call;
+  };
+}