add functionArgs

nodes/1_lib/source/detangled/1_foundation.nix

@@ -77,6 +77,25 @@ let
   isFunction = f: builtins.isFunction f ||
     (f ? __functor && isFunction (f.__functor f));
     
+  /**
+    Extract the expected function arguments from a function.
+    This works both with nix-native { a, b ? foo, ... }: style
+    functions and functions with args set with 'setFunctionArgs'. It
+    has the same return type and semantics as builtins.functionArgs.
+    setFunctionArgs : (a → b) → Map String Bool.
+
+
+    # Inputs
+
+    `f`
+
+    : 1\. Function argument
+  */
+  functionArgs = f:
+    if f ? __functor
+    then f.__functionArgs or (functionArgs (f.__functor f))
+    else builtins.functionArgs f;
+    
   /**
     Print a warning before returning the second argument. This function behaves
     like `builtins.trace`, but requires a string message and formats it as a
@@ -110,5 +129,6 @@ in
     loadStatic   = loadStatic;
     foldr        = foldr;
     isFunction   = isFunction;
+    functionArgs = functionArgs;
     warn         = warn;
   }