Simplify how anonymous functions are parsed

Updates the way that we handle passing higher order functions into egglog
to remove some previous metaprogramming magic and replace it with a simpler
algorithm that just removes any unbound variables left in a function and hoists
them as args to the function.

Author: saulshanabrook

docs/changelog.md

@@ -9,6 +9,8 @@ _This project uses semantic versioning_
     Also changes the representation to be an index into a list instead of the ID, making egglog programs more deterministic.
   - Prefix constant declerations and unbound variables to not shadow let variables
   - BREAKING: Remove `simplify` since it was removed upstream. You can manually replace it with an insert, run, then extract.
+- Change how anonymous functions are converted to remove metaprogramming and lift only the unbound variables as args
+- Add support for getting the "value" of a function type with `.eval()`, i.e. `assert UnstableFn(f).eval() == f`.
 
 ## 10.0.2 (2025-06-22)
 

python/egglog/builtins.py

@@ -8,16 +8,18 @@
 from collections.abc import Callable
 from fractions import Fraction
 from functools import partial, reduce
+from inspect import signature
 from types import FunctionType, MethodType
 from typing import TYPE_CHECKING, Generic, Protocol, TypeAlias, TypeVar, cast, overload
 
 from typing_extensions import TypeVarTuple, Unpack
 
-from .conversion import convert, converter, get_type_args
+from egglog.declarations import TypedExprDecl
+
+from .conversion import convert, converter, get_type_args, resolve_literal
 from .declarations import *
-from .egraph import BaseExpr, BuiltinExpr, expr_fact, function, get_current_ruleset, method
-from .functionalize import functionalize
-from .runtime import RuntimeClass, RuntimeExpr, RuntimeFunction
+from .egraph import BaseExpr, BuiltinExpr, _add_default_rewrite_inner, expr_fact, function, get_current_ruleset, method
+from .runtime import RuntimeClass, RuntimeExpr, RuntimeFunction, resolve_type_annotation_mutate
 from .thunk import Thunk
 
 if TYPE_CHECKING:
@@ -1022,46 +1024,89 @@ def __init__(self, f, *partial) -> None: ...
     @method(egg_fn="unstable-app")
     def __call__(self, *args: Unpack[TS]) -> T: ...
 
+    @method(preserve=True)
+    def eval(self) -> Callable[[Unpack[TS]], T]:
+        """
+        If this is a constructor, returns either the callable directly or a `functools.partial` function if args are provided.
+        """
+        assert isinstance(self, RuntimeExpr)
+        match self.__egg_typed_expr__.expr:
+            case PartialCallDecl(CallDecl() as call):
+                fn, args = _deconstruct_call_decl(self.__egg_decls_thunk__, call)
+                if not args:
+                    return fn
+                return partial(fn, *args)
+        msg = "UnstableFn can only be evaluated if it is a function or a partial application of a function."
+        raise BuiltinEvalError(msg)
+
+
+def _deconstruct_call_decl(
+    decls_thunk: Callable[[], Declarations], call: CallDecl
+) -> tuple[Callable, tuple[object, ...]]:
+    """
+    Deconstructs a CallDecl into a runtime callable and its arguments.
+    """
+    args = call.args
+    arg_exprs = tuple(RuntimeExpr(decls_thunk, Thunk.value(a)) for a in args)
+    egg_bound = (
+        JustTypeRef(call.callable.class_name, call.bound_tp_params or ())
+        if isinstance(call.callable, (ClassMethodRef, InitRef, ClassVariableRef))
+        else None
+    )
+    if isinstance(call.callable, InitRef):
+        return RuntimeClass(
+            decls_thunk,
+            TypeRefWithVars(
+                call.callable.class_name,
+            ),
+        ), arg_exprs
+    return RuntimeFunction(decls_thunk, Thunk.value(call.callable), egg_bound), arg_exprs
+
 
 # Method Type is for builtins like __getitem__
 converter(MethodType, UnstableFn, lambda m: UnstableFn(m.__func__, m.__self__))
 converter(RuntimeFunction, UnstableFn, UnstableFn)
 converter(partial, UnstableFn, lambda p: UnstableFn(p.func, *p.args))
 
 
-def _convert_function(a: FunctionType) -> UnstableFn:
+def _convert_function(fn: FunctionType) -> UnstableFn:
     """
-    Converts a function type to an unstable function
+    Converts a function type to an unstable function. This function will be an anon function in egglog.
 
-    Would just be UnstableFn(function(a)) but we have to look for any nonlocals and globals
-    which are runtime expressions with `var`s in them and add them as args to the function
+    Would just be UnstableFn(function(a)) but we have to account for unbound vars within the body.
+
+    This means that we have to turn all of those unbound vars into args to the function, and then
+    partially apply them, alongside creating a default rewrite for the function.
     """
-    # Update annotations of a to be the type we are trying to convert to
-    return_tp, *arg_tps = get_type_args()
-    a.__annotations__ = {
-        "return": return_tp,
-        # The first varnames should always be the arg names
-        **dict(zip(a.__code__.co_varnames, arg_tps, strict=False)),
-    }
-    # Modify name to make it unique
-    # a.__name__ = f"{a.__name__} {hash(a.__code__)}"
-    transformed_fn = functionalize(a, value_to_annotation)
-    assert isinstance(transformed_fn, partial)
-    return UnstableFn(
-        function(ruleset=get_current_ruleset(), use_body_as_name=True, subsume=True)(transformed_fn.func),
-        *transformed_fn.args,
+    decls = Declarations()
+    return_type, *arg_types = [resolve_type_annotation_mutate(decls, tp) for tp in get_type_args()]
+    arg_names = [p.name for p in signature(fn).parameters.values()]
+    arg_decls = [
+        TypedExprDecl(tp.to_just(), UnboundVarDecl(name)) for name, tp in zip(arg_names, arg_types, strict=True)
+    ]
+    res = resolve_literal(
+        return_type, fn(*(RuntimeExpr.__from_values__(decls, a) for a in arg_decls)), Thunk.value(decls)
     )
+    res_expr = res.__egg_typed_expr__
+    decls |= res
+    # these are all the args that appear in the body that are not bound by the args of the function
+    unbound_vars = list(collect_unbound_vars(res_expr) - set(arg_decls))
+    # prefix the args with them
+    fn_ref = UnnamedFunctionRef(tuple(unbound_vars + arg_decls), res_expr)
+    rewrite_decl = DefaultRewriteDecl(fn_ref, res_expr.expr, subsume=True)
+    ruleset_decls = _add_default_rewrite_inner(decls, rewrite_decl, get_current_ruleset())
+    ruleset_decls |= res
 
-
-def value_to_annotation(a: object) -> type | None:
-    # only lift runtime expressions (which could contain vars) not any other nonlocals/globals we use in the function
-    if not isinstance(a, RuntimeExpr):
-        return None
-    return cast("type", RuntimeClass(Thunk.value(a.__egg_decls__), a.__egg_typed_expr__.tp.to_var()))
+    fn = RuntimeFunction(Thunk.value(decls), Thunk.value(fn_ref))
+    return UnstableFn(fn, *(RuntimeExpr.__from_values__(decls, v) for v in unbound_vars))
 
 
 converter(FunctionType, UnstableFn, _convert_function)
 
+##
+# Utility Functions
+##
+
 
 def _extract_lit(e: BaseExpr) -> LitType:
     """

python/egglog/declarations.py

@@ -77,6 +77,7 @@
     "UnboundVarDecl",
     "UnionDecl",
     "UnnamedFunctionRef",
+    "collect_unbound_vars",
     "replace_typed_expr",
     "upcast_declerations",
 ]
@@ -683,6 +684,28 @@ def _inner(typed_expr: TypedExprDecl) -> TypedExprDecl:
     return _inner(typed_expr)
 
 
+def collect_unbound_vars(typed_expr: TypedExprDecl) -> set[TypedExprDecl]:
+    """
+    Returns the set of all unbound vars
+    """
+    seen = set[TypedExprDecl]()
+    unbound_vars = set[TypedExprDecl]()
+
+    def visit(typed_expr: TypedExprDecl) -> None:
+        if typed_expr in seen:
+            return
+        seen.add(typed_expr)
+        match typed_expr.expr:
+            case CallDecl(_, args) | PartialCallDecl(CallDecl(_, args)):
+                for arg in args:
+                    visit(arg)
+            case UnboundVarDecl(_):
+                unbound_vars.add(typed_expr)
+
+    visit(typed_expr)
+    return unbound_vars
+
+
 ##
 # Schedules
 ##

python/egglog/egraph.py

@@ -29,6 +29,7 @@
 
 from . import bindings
 from .conversion import *
+from .conversion import convert_to_same_type, resolve_literal
 from .declarations import *
 from .egraph_state import *
 from .ipython_magic import IN_IPYTHON
@@ -281,7 +282,6 @@ def function(
     mutates_first_arg: bool = ...,
     unextractable: bool = ...,
     ruleset: Ruleset | None = ...,
-    use_body_as_name: bool = ...,
     subsume: bool = ...,
 ) -> Callable[[CONSTRUCTOR_CALLABLE], CONSTRUCTOR_CALLABLE]: ...
 
@@ -467,7 +467,7 @@ def _generate_class_decls(  # noqa: C901,PLR0912
             decls.set_function_decl(ref, decl)
             continue
         try:
-            _, add_rewrite = _fn_decl(
+            add_rewrite = _fn_decl(
                 decls,
                 egg_fn,
                 ref,
@@ -505,19 +505,17 @@ class _FunctionConstructor:
     merge: Callable[[object, object], object] | None = None
     unextractable: bool = False
     ruleset: Ruleset | None = None
-    use_body_as_name: bool = False
     subsume: bool = False
 
     def __call__(self, fn: Callable) -> RuntimeFunction:
         return RuntimeFunction(*split_thunk(Thunk.fn(self.create_decls, fn)))
 
     def create_decls(self, fn: Callable) -> tuple[Declarations, CallableRef]:
         decls = Declarations()
-        ref = None if self.use_body_as_name else FunctionRef(fn.__name__)
-        ref, add_rewrite = _fn_decl(
+        add_rewrite = _fn_decl(
             decls,
             self.egg_fn,
-            ref,
+            ref := FunctionRef(fn.__name__),
             fn,
             self.hint_locals,
             self.cost,
@@ -535,8 +533,7 @@ def create_decls(self, fn: Callable) -> tuple[Declarations, CallableRef]:
 def _fn_decl(
     decls: Declarations,
     egg_name: str | None,
-    # If ref is Callable, then generate the ref from the function name
-    ref: FunctionRef | MethodRef | PropertyRef | ClassMethodRef | InitRef | None,
+    ref: FunctionRef | MethodRef | PropertyRef | ClassMethodRef | InitRef,
     fn: object,
     # Pass in the locals, retrieved from the frame when wrapping,
     # so that we support classes and function defined inside of other functions (which won't show up in the globals)
@@ -549,7 +546,7 @@ def _fn_decl(
     ruleset: Ruleset | None = None,
     unextractable: bool = False,
     reverse_args: bool = False,
-) -> tuple[CallableRef, Callable[[], None]]:
+) -> Callable[[], None]:
     """
     Sets the function decl for the function object and returns the ref as well as a thunk that sets the default callable.
     """
@@ -619,50 +616,39 @@ def _fn_decl(
 
     # defer this in generator so it doesn't resolve for builtins eagerly
     args = (TypedExprDecl(tp.to_just(), UnboundVarDecl(name)) for name, tp in zip(arg_names, arg_types, strict=True))
-    res_ref: FunctionRef | MethodRef | ClassMethodRef | PropertyRef | InitRef | UnnamedFunctionRef
-    res_thunk: Callable[[], object]
-    # If we were not passed in a ref, this is an unnamed funciton, so eagerly compute the value and use that to refer to it
-    if not ref:
-        tuple_args = tuple(args)
-        res = _create_default_value(decls, ref, fn, tuple_args, ruleset)
-        assert isinstance(res, RuntimeExpr)
-        res_ref = UnnamedFunctionRef(tuple_args, res.__egg_typed_expr__)
-        decls._unnamed_functions.add(res_ref)
-        res_thunk = Thunk.value(res)
 
+    return_type_is_eqsort = (
+        not decls._classes[return_type.name].builtin if isinstance(return_type, TypeRefWithVars) else False
+    )
+    is_constructor = not is_builtin and return_type_is_eqsort and merged is None
+    signature_ = FunctionSignature(
+        return_type=None if mutates_first_arg else return_type,
+        var_arg_type=var_arg_type,
+        arg_types=arg_types,
+        arg_names=arg_names,
+        arg_defaults=tuple(a.__egg_typed_expr__.expr if a is not None else None for a in arg_defaults),
+        reverse_args=reverse_args,
+    )
+    decl: ConstructorDecl | FunctionDecl
+    if is_constructor:
+        decl = ConstructorDecl(signature_, egg_name, cost, unextractable)
     else:
-        return_type_is_eqsort = (
-            not decls._classes[return_type.name].builtin if isinstance(return_type, TypeRefWithVars) else False
-        )
-        is_constructor = not is_builtin and return_type_is_eqsort and merged is None
-        signature_ = FunctionSignature(
-            return_type=None if mutates_first_arg else return_type,
-            var_arg_type=var_arg_type,
-            arg_types=arg_types,
-            arg_names=arg_names,
-            arg_defaults=tuple(a.__egg_typed_expr__.expr if a is not None else None for a in arg_defaults),
-            reverse_args=reverse_args,
+        if cost is not None:
+            msg = "Cost can only be set for constructors"
+            raise ValueError(msg)
+        if unextractable:
+            msg = "Unextractable can only be set for constructors"
+            raise ValueError(msg)
+        decl = FunctionDecl(
+            signature=signature_,
+            egg_name=egg_name,
+            merge=merged.__egg_typed_expr__.expr if merged is not None else None,
+            builtin=is_builtin,
         )
-        decl: ConstructorDecl | FunctionDecl
-        if is_constructor:
-            decl = ConstructorDecl(signature_, egg_name, cost, unextractable)
-        else:
-            if cost is not None:
-                msg = "Cost can only be set for constructors"
-                raise ValueError(msg)
-            if unextractable:
-                msg = "Unextractable can only be set for constructors"
-                raise ValueError(msg)
-            decl = FunctionDecl(
-                signature=signature_,
-                egg_name=egg_name,
-                merge=merged.__egg_typed_expr__.expr if merged is not None else None,
-                builtin=is_builtin,
-            )
-        res_ref = ref
-        decls.set_function_decl(ref, decl)
-        res_thunk = Thunk.fn(_create_default_value, decls, ref, fn, args, ruleset, context=f"creating {ref}")
-    return res_ref, Thunk.fn(_add_default_rewrite_function, decls, res_ref, return_type, ruleset, res_thunk, subsume)
+    decls.set_function_decl(ref, decl)
+    return Thunk.fn(
+        _add_default_rewrite_function, decls, ref, fn, args, ruleset, subsume, return_type, context=f"creating {ref}"
+    )
 
 
 # Overload to support aritys 0-4 until variadic generic support map, so we can map from type to value
@@ -736,35 +722,24 @@ def _constant_thunk(
     return decls, TypedExprDecl(type_ref.to_just(), CallDecl(callable_ref))
 
 
-def _create_default_value(
+def _add_default_rewrite_function(
     decls: Declarations,
-    ref: CallableRef | None,
+    ref: FunctionRef | MethodRef | PropertyRef | ClassMethodRef | InitRef,
     fn: Callable,
     args: Iterable[TypedExprDecl],
     ruleset: Ruleset | None,
-) -> object:
+    subsume: bool,
+    res_type: TypeOrVarRef,
+) -> None:
     args: list[object] = [RuntimeExpr.__from_values__(decls, a) for a in args]
 
     # If this is a classmethod, add the class as the first arg
     if isinstance(ref, ClassMethodRef):
         tp = decls.get_paramaterized_class(ref.class_name)
         args.insert(0, RuntimeClass(Thunk.value(decls), tp))
     with set_current_ruleset(ruleset):
-        return fn(*args)
-
-
-def _add_default_rewrite_function(
-    decls: Declarations,
-    ref: CallableRef,
-    res_type: TypeOrVarRef,
-    ruleset: Ruleset | None,
-    value_thunk: Callable[[], object],
-    subsume: bool,
-) -> None:
-    """
-    Helper functions that resolves a value thunk to create the default value.
-    """
-    _add_default_rewrite(decls, ref, res_type, value_thunk(), ruleset, subsume)
+        res = fn(*args)
+    _add_default_rewrite(decls, ref, res_type, res, ruleset, subsume)
 
 
 def _add_default_rewrite(
@@ -784,14 +759,21 @@ def _add_default_rewrite(
         return
     resolved_value = resolve_literal(type_ref, default_rewrite, Thunk.value(decls))
     rewrite_decl = DefaultRewriteDecl(ref, resolved_value.__egg_typed_expr__.expr, subsume)
+    ruleset_decls = _add_default_rewrite_inner(decls, rewrite_decl, ruleset)
+    ruleset_decls |= resolved_value
+
+
+def _add_default_rewrite_inner(
+    decls: Declarations, rewrite_decl: DefaultRewriteDecl, ruleset: Ruleset | None
+) -> Declarations:
     if ruleset:
         ruleset_decls = ruleset._current_egg_decls
         ruleset_decl = ruleset.__egg_ruleset__
     else:
         ruleset_decls = decls
         ruleset_decl = decls.default_ruleset
     ruleset_decl.rules.append(rewrite_decl)
-    ruleset_decls |= resolved_value
+    return ruleset_decls
 
 
 def _last_param_variable(params: list[Parameter]) -> bool: