wip: first attempt

desys.nix

@@ -2,26 +2,45 @@
 #
 # SPDX-License-Identifier: Unlicense
 let
-  l = builtins;
+  l = builtins // {
+    # taken from `nixpkgs.lib.debug`
+    traceIf =
+      # Predicate to check
+      pred:
+      # Message that should be traced
+      msg:
+      # Value to return
+      x: if pred then l.trace msg x else x;
+  };
+
+
+  cutat = 3;
+  pad = n: l.concatStringsSep "" (l.genList (_: "\t") n);
   /*
   A helper function which hides the complexities of dealing
   with 'system' properly from you, while still providing
   escape hatches when dealing with cross-compilation.
   */
-  deSystemize = let
-    iteration = cutoff: system: fragment:
+  deSystemize = debug: let
+    iteration = name: cutoff: system: fragment:
       if ! (l.isAttrs fragment) || cutoff == 0
       then fragment
       else let
-        recursed = l.mapAttrs (_: iteration (cutoff - 1) system) fragment;
+        recursed = l.mapAttrs (n:
+          l.traceIf debug "deSys:${pad (cutat - cutoff)} visit ${n}"
+          iteration n (cutoff - 1) system
+        ) fragment;
       in
         if l.hasAttr "${system}" fragment
         then
+          l.traceIf debug "deSys:${pad (cutat - cutoff)} hoist '${system}' onto '${name}' for direct access"
+        (
           if l.isFunction fragment.${system}
           then recursed // {__functor = _: fragment.${system};}
           else recursed // fragment.${system}
+        )
         else recursed;
   in
-    iteration 3;
+    iteration "." cutat;
 in
   deSystemize

flake.nix

@@ -3,28 +3,50 @@
 # SPDX-License-Identifier: Unlicense
 {
   description = "Nix flakes with `systems` à la carte.";
-  outputs = {self}: {
-    __functor = self: self.lib.noSys;
+  outputs = {self}: let
+    l = builtins // {
+      # taken from `nixpkgs.lib.debug`
+      traceIf =
+        # Predicate to check
+        pred:
+        # Message that should be traced
+        msg:
+        # Value to return
+        x: if pred then l.trace msg x else x;
+    };
 
-    lib.noSys = inputs @ {systems ? import ./systems.nix, ...}: f: let
+    deSys = import ./desys.nix;
+    eachSys = import ./eachSys.nix;
+    noSys = debug: inputs @ {systems ? import ./systems.nix, ...}: f: let
       systems' =
-        if builtins.isPath systems || systems ? outPath
+        if l.isPath systems || systems ? outPath
         then import systems
         else systems;
     in
-      self.lib.eachSys systems' (sys: let
+      l.traceIf debug "systems ${l.concatStringsSep ", " systems'}"
+      eachSys systems' (sys: let
         f' = inputs: let
           # mapAttrs to deSys up to the same depths as in `self`
-          inputs' = builtins.mapAttrs (_: self.lib.deSys sys) (builtins.removeAttrs inputs ["self"]);
-          self' = self.lib.deSys sys (builtins.removeAttrs inputs.self ["inputs"]);
-        in
+          inputs' = l.mapAttrs (_: deSys debug sys) (l.removeAttrs inputs ["self"]);
+          self' = deSys debug sys (l.removeAttrs inputs.self ["inputs"]);
           # must be recombined after `deSys` to avoid infinite recursion
-          f (inputs' // {self = self';});
+          args = inputs' // {self = self';};
+        in
+          f args;
       in
         f' inputs);
 
-    lib.deSys = import ./desys.nix;
-    lib.eachSys = import ./eachSys.nix;
+  in {
+
+    debug = false;
+    __functor = {debug, ... }: noSys debug;
+
+    lib = {
+      inherit eachSys;
+      # no debug
+      deSys = deSys false;
+      noSys = noSys false;
+    };
 
     templates.default = {
       path = ./tmpl;

tmpl/flake.nix

@@ -1,11 +1,11 @@
 {
-  inputs.nosys.url = "github:divnix/nosys";
+  inputs.nosys.url = "path:../.";
 
   inputs.systems.url = "path:./flake/systems.nix";
   inputs.systems.flake = false;
 
-  outputs = inputs @ {nosys, ...}: let
+  outputs = inputs @ {nosys, nixpkgs, ...}: let
     outputs = import ./flake/outputs.nix;
   in
-    nosys inputs outputs;
+    (nosys // {debug = true;}) inputs outputs;
 }

tmpl/flake/outputs.nix

@@ -1,2 +1,3 @@
-{self, ...}: {
+{self, nixpkgs, ...}: {
+  packages = {inherit (nixpkgs.legacyPackages) hello;};
 }