Syntax: a toplevel declaration
%object S(a1,...,an).b.
where
  S: signature name
  a1, ..., an, b: names declared in S

Semantics: For ground A1, ..., An, the use of S(A1,...,An) within an object O adds a structure
%struct I : S = {a1 := A1. ... an := An.}.
and then elaborates to
I.b
where I is a fresh (internal) name.
If S(A1,...,An) occurs multiple times, only one structure I is generated.

Example:

%sig List = {
  a    : type.
  list : type.
  nil  : list.
  cons : a -> list -> list.
}.

%sig Map = {
  a   : type.
  b   : type.
  f   : a -> b -> type.
  map : List(a) -> List(b) -> type.
}.

%sig Nat = {
  nat  : type.
  z    : nat.
  succ : nat -> nat.
  F    : nat -> nat -> type.
}.

%object List(a).list.
%object Map(a,b,f).map.
%object Nat.nat.

%solve Map(Nat,Nat,F) (List(Nat).cons Nat.z List(Nat).nil) L.


Possible improvement: inference of parameters
%solve Map(Nat,Nat,F) (List.cons Nat.z List.nil) L.