Make Expr type explicit, add Literal constructor

effectful/internals/bootstrap.py

@@ -11,6 +11,7 @@
     Symbol,
     Term,
     Variable,
+    Literal,
 )
 
 from ..ops import core
@@ -53,6 +54,11 @@ class _BaseVariable(Generic[T]):
     type: Type[T]
 
 
+@dataclasses.dataclass
+class _BaseLiteral(Generic[T]):
+    value: T
+
+
 @runtime.weak_memoize
 def base_define(m: Type[T] | Callable[Q, T]) -> Operation[..., T]:
     if not typing.TYPE_CHECKING:
@@ -82,6 +88,7 @@ def defop(fn: Callable[..., S]) -> _BaseOperation[..., S]:
 core.register(core.define(Operation), None, _BaseOperation)
 core.register(core.define(Term), None, _BaseTerm)
 core.register(core.define(Variable), None, _BaseVariable)
+core.register(core.define(Literal), None, _BaseLiteral)
 core.register(core.define(Interpretation), None, dict)
 core.register(core.define(Symbol), None, str)
 core.register(core.define(Context), None, dict)

effectful/ops/core.py

@@ -22,11 +22,18 @@ def default(self, *args: P.args, **kwargs: P.kwargs) -> T_co: ...
 Interpretation = Mapping[Operation[..., T], Callable[..., V]]
 
 
+class Literal(Protocol[T]):
+    value: T
+
+
+Expr = Literal[T] | "Term[T]" | "Variable[T]"
+
+
 @typing.runtime_checkable
 class Term(Protocol[T]):
     op: Operation[..., T]
-    args: Iterable["Term[T]" | T | "Variable[T]"]
-    kwargs: Mapping[str, "Term[T]" | T | "Variable[T]"]
+    args: Iterable[Expr[T]]
+    kwargs: Mapping[str, Expr[T]]
 
 
 Symbol = str  # TODO replace with extensional protocol type