Use a dedicated type to represent interpreted-function valuesscratch/interpreted-function

Change `function` so that when evaluating #'(lambda ...)
we return an object of type `interpreted-function` rather than
a list starting with one of `lambda` or `closure`.
The new type reuses the existing PVEC_CLOSURE (nee PVEC_COMPILED)
tag and tries to align the corresponding elements:

- the arglist, the docstring, and the interactive-form go in the
  same slots as for byte-code functions.
- the body of the function goes in the slot used for the bytecode string.
- the lexical context goes in the slot used for the constants of
  bytecoded functions.

The first point above means that `help-function-arglist`,
`documentation`, and `interactive-form`s don't need to
distinguish interpreted and bytecode functions any more.

Main benefits of the change:

- We can now reliably distinguish a list from a function value.
- `cl-defmethod` can dispatch on `interactive-function` and `closure`.
  Dispatch on `function` also works now for interpreted functions but still
  won't work for functions represented as lists or as symbols, of course.
- Function values are now self-evaluating.  That was alrready the case
  when byte-compiled, but not when interpreted since
  (eval '(closure ...)) signals a void-function error.
  That also avoids false-positive warnings about "don't quote your lambdas"
  when doing things like `(mapcar ',func ...)`.

* src/eval.c (Fmake_interpreted_closure): New function.
(Ffunction): Use it and change calling convention of
`Vinternal_make_interpreted_closure_function`.
(FUNCTIONP, Fcommandp, eval_sub, funcall_general, funcall_lambda)
(Ffunc_arity, lambda_arity): Simplify.
(funcall_lambda): Adjust to new representation.
(syms_of_eval): `defsubr` the new function.  Remove definition of `Qclosure`.

* lisp/emacs-lisp/cconv.el (cconv-make-interpreted-closure):
Change calling convention and use `make-interpreted-closure`.

* src/data.c (Fcl_type_of): Distinguish `byte-code-function`s from
`interpreted-function`s.
(Fclosurep, finterpreted_function_p): New functions.
(Fbyte_code_function_p): Don't be confused by `interpreted-function`s.
(Finteractive_form, Fcommand_modes): Simplify.
(syms_of_data): Define new type symbols and `defsubr` the two
new functions.

* lisp/emacs-lisp/cl-print.el (cl-print-object) <interpreted-function>:
New method.

* lisp/emacs-lisp/oclosure.el (oclosure): Refine the parent
to be `closure`.
(oclosure--fix-type, oclosure-type): Simplify.
(oclosure--copy, oclosure--get, oclosure--set): Adjust to
new representation.

* src/callint.c (Fcall_interactively): Adjust to new representation.

* src/lread.c (bytecode_from_rev_list):

* lisp/simple.el (function-documentation):
* lisp/help.el (help-function-arglist): Remove the old `closure` case
and adjust the byte-code case so it handles `interpreted-function`s.

* lisp/emacs-lisp/cl-preloaded.el (closure): New type.
(byte-code-function): Add it as a parent.
(interpreted-function): Adjust parent (the type itself was already
added earlier by accident).

* lisp/emacs-lisp/bytecomp.el (byte-compile--reify-function): Adjust to
new representation.
(byte-compile): Use `interpreted-function-p`.

* lisp/emacs-lisp/byte-opt.el (byte-compile-inline-expand): Adjust to
new representation.
(side-effect-free-fns): Add `interpreted-function-p` and `closurep`.

* src/profiler.c (trace_hash, ffunction_equal): Simplify.
* lisp/profiler.el (profiler-function-equal): Simplify.

* lisp/emacs-lisp/nadvice.el (advice--interactive-form-1):
Use `interpreted-function-p`; adjust to new representation; and take
advantage of the fact that function values are now self-evaluating.

* lisp/emacs-lisp/lisp-mode.el (closure):
Remove `lisp-indent-function` property.

* lisp/emacs-lisp/disass.el (disassemble-internal): Adjust to
new representation.
* lisp/emacs-lisp/edebug.el (edebug--strip-instrumentation):
Use `interpreted-function-p`.
* lisp/emacs-lisp/comp-common.el (comp-known-type-specifiers):
Add `closurep` and `interpreted-function-p`.

* test/lisp/help-fns-tests.el (help-fns-test-lisp-defun): Adjust to
more precise type info in `describe-function`.
* test/lisp/erc/resources/erc-d/erc-d-tests.el (erc-d--render-entries):
Use `interpreted-function-p`.
* test/lisp/emacs-lisp/macroexp-resources/vk.el (vk-f4, vk-f5):
Don't hardcode function values.

* doc/lispref/functions.texi (Anonymous Functions): Don't suggest that
function values are lists.  Reword "self-quoting" to reflect the
fact that #' doesn't return the exact same object.  Update examples
with the new shape of the return value.

* doc/lispref/variables.texi (Lexical Binding):
* doc/lispref/lists.texi (Rearrangement):
* doc/lispref/control.texi (Handling Errors): Update examples to reflect
new representation of function values.

1 files changed, 23 insertions, 13 deletions

diff --git a/doc/lispref/functions.texi b/doc/lispref/functions.texi
index ff635fc54b2..c57de08460f 100644
--- a/doc/lispref/functions.texi
+++ b/doc/lispref/functions.texi
@@ -130,7 +130,7 @@ it also encloses an environment of lexical variable bindings.
 
 @item byte-code function
 A function that has been compiled by the byte compiler.
-@xref{Byte-Code Type}.
+@xref{Closure Type}.
 
 @item autoload object
 @cindex autoload object
@@ -227,6 +227,16 @@ Compilation}), or natively-compiled (@pxref{Native Compilation}), or
 a function loaded from a dynamic module (@pxref{Dynamic Modules}).
 @end defun
 
+@defun interpreted-function-p object
+This function returns @code{t} if @var{object} is an interpreted function.
+@end defun
+
+@defun closurep object
+This function returns @code{t} if @var{object} is a closure, which is
+a particular kind of function object.  Currently closures are used
+for all byte-code functions and all interpreted functions.
+@end defun
+
 @defun subr-arity subr
 This works like @code{func-arity}, but only for built-in functions and
 without symbol indirection.  It signals an error for non-built-in
@@ -1136,8 +1146,7 @@ Functions}).  @xref{describe-symbols example}, for a realistic example
 of this.
 
   When defining a lambda expression that is to be used as an anonymous
-function, you can in principle use any method to construct the list.
-But typically you should use the @code{lambda} macro, or the
+function, you should use the @code{lambda} macro, or the
 @code{function} special form, or the @code{#'} read syntax:
 
 @defmac lambda args [doc] [interactive] body@dots{}
@@ -1145,17 +1154,18 @@ This macro returns an anonymous function with argument list
 @var{args}, documentation string @var{doc} (if any), interactive spec
 @var{interactive} (if any), and body forms given by @var{body}.
 
-Under dynamic binding, this macro effectively makes @code{lambda}
-forms self-quoting: evaluating a form whose @sc{car} is @code{lambda}
-yields the form itself:
+For example, this macro makes @code{lambda} forms almost self-quoting:
+evaluating a form whose @sc{car} is @code{lambda} yields a value that is
+almost like the form itself:
 
 @example
 (lambda (x) (* x x))
-     @result{} (lambda (x) (* x x))
+     @result{} #f(lambda (x) :dynbind (* x x))
 @end example
 
-Note that when evaluating under lexical binding the result is a
-closure object (@pxref{Closures}).
+When evaluating under lexical binding the result is a similar
+closure object, where the @code{:dynbind} marker is replaced by the
+captured variables (@pxref{Closures}).
 
 The @code{lambda} form has one other effect: it tells the Emacs
 evaluator and byte-compiler that its argument is a function, by using
@@ -1164,8 +1174,8 @@ evaluator and byte-compiler that its argument is a function, by using
 
 @defspec function function-object
 @cindex function quoting
-This special form returns @var{function-object} without evaluating it.
-In this, it is similar to @code{quote} (@pxref{Quoting}).  But unlike
+This special form returns the function value of the @var{function-object}.
+In many ways, it is similar to @code{quote} (@pxref{Quoting}).  But unlike
 @code{quote}, it also serves as a note to the Emacs evaluator and
 byte-compiler that @var{function-object} is intended to be used as a
 function.  Assuming @var{function-object} is a valid lambda
@@ -1495,7 +1505,7 @@ distinguish between a function cell that is void and one set to
 @group
 (defun bar (n) (+ n 2))
 (symbol-function 'bar)
-     @result{} (lambda (n) (+ n 2))
+     @result{} #f(lambda (n) [t] (+ n 2))
 @end group
 @group
 (fset 'baz 'bar)
@@ -1608,7 +1618,7 @@ argument list and body forms as the remaining elements:
 @example
 ;; @r{lexical binding is enabled.}
 (lambda (x) (* x x))
-     @result{} (closure (t) (x) (* x x))
+     @result{} #f(lambda (x) [t] (* x x))
 @end example
 
 @noindent