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Best idea I've come up with to do this is to have yants export a function that generates a type checking pop. This pop will simply have an extension that does nothing but type check a series of values. If there are any problems, yants check functions will throw errors, otherwise the extension can just return an empty attrset. This could be implemented in yants itself.

nix-repl> pop.lib.pop { supers = [ { a = throw "err"; b = 5; } ]; }
error: err

An attribute in a pop containing an error shouldn't error out the entire pop. Other attributes should still be accessible even if one attribute errors out.

The following code should print out 5, but it would just error out now.

p = pop.lib.pop { supers = [ { a = throw "err"; b = 5; } ]; }
p.b

cc @fare

let
  a = pop { defaults.n = 1; extension = self: super: { n = super.n + 1; }; }
  b = pop { supers = [ a ]; }
in
  b.n

evaluates to 3 when it should be 2

Many times there are attributes you want to include in a POP for utility purposes, but they shouldn't be in the end result(after unpopping). There should be some way to mark certain attributes as special.

This could also replace #1 since you can just add extenders in a pop's extension and mark those attributes as "special", so they get removed when unpopping.

p = pop {
  defaults.value = 0;
  extension = self: super: {
    # Mark increment as "special" somehow
    increment = pop { supers = [ self ]; extension = _: _: { value = super.value + 1; }; };
  };
}
unpop (p.increment.increment) => { value = 2; }

or with #7

pop {
  defaults.value = 0;
  extension = self: super: {
    increment = self (self: super: { value = super.value + 1; });
  };
}

cc @fare