mirror of
https://git.savannah.gnu.org/git/emacs.git
synced 2024-11-30 08:09:04 +00:00
802 lines
31 KiB
EmacsLisp
802 lines
31 KiB
EmacsLisp
;;; generator.el --- generators -*- lexical-binding: t -*-
|
|
|
|
;; Copyright (C) 2015-2024 Free Software Foundation, Inc.
|
|
|
|
;; Author: Daniel Colascione <dancol@dancol.org>
|
|
;; Keywords: extensions, elisp
|
|
;; Package: emacs
|
|
|
|
;; This file is part of GNU Emacs.
|
|
|
|
;; GNU Emacs is free software: you can redistribute it and/or modify
|
|
;; it under the terms of the GNU General Public License as published by
|
|
;; the Free Software Foundation, either version 3 of the License, or
|
|
;; (at your option) any later version.
|
|
|
|
;; GNU Emacs is distributed in the hope that it will be useful,
|
|
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
;; GNU General Public License for more details.
|
|
|
|
;; You should have received a copy of the GNU General Public License
|
|
;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
|
|
|
|
;;; Commentary:
|
|
|
|
;; This package implements generators for Emacs Lisp through a
|
|
;; continuation-passing transformation. It provides essentially the
|
|
;; same generator API and iterator facilities that Python and
|
|
;; JavaScript ES6 provide.
|
|
;;
|
|
;; `iter-lambda' and `iter-defun' work like `lambda' and `defun',
|
|
;; except that they evaluate to or define, respectively, generator
|
|
;; functions. These functions, when called, return an iterator.
|
|
;; An iterator is an opaque object that generates a sequence of
|
|
;; values. Callers use `iter-next' to retrieve the next value from
|
|
;; the sequence; when the sequence is exhausted, `iter-next' will
|
|
;; raise the `iter-end-of-sequence' condition.
|
|
;;
|
|
;; Generator functions are written like normal functions, except that
|
|
;; they can invoke `iter-yield' to suspend themselves and return a
|
|
;; value to callers; this value becomes the return value of
|
|
;; `iter-next'. On the next call to `iter-next', execution of the
|
|
;; generator function resumes where it left off. When a generator
|
|
;; function returns normally, the `iter-next' raises
|
|
;; `iter-end-of-sequence' with the value the function returned.
|
|
;;
|
|
;; `iter-yield-from' yields all the values from another iterator; it
|
|
;; then evaluates to the value the sub-iterator returned normally.
|
|
;; This facility is useful for functional composition of generators
|
|
;; and for implementing coroutines.
|
|
;;
|
|
;; `iter-yield' is illegal inside the UNWINDFORMS of an
|
|
;; `unwind-protect' for various sordid internal reasons documented in
|
|
;; the code.
|
|
;;
|
|
;; N.B. Each call to a generator function generates a *new* iterator,
|
|
;; and each iterator maintains its own internal state.
|
|
;;
|
|
;; This raw form of iteration is general, but a bit awkward to use, so
|
|
;; this library also provides some convenience functions:
|
|
;;
|
|
;; `iter-do' is like `dolist', except that instead of walking a list,
|
|
;; it walks an iterator. `cl-loop' is also extended with a new
|
|
;; keyword, `iter-by', that iterates over an iterator.
|
|
;;
|
|
|
|
;;; Implementation:
|
|
|
|
;;
|
|
;; The internal CPS transformation code uses the cps- namespace.
|
|
;; Iteration functions use the `iter-' namespace. Generator functions
|
|
;; are somewhat less efficient than conventional elisp routines,
|
|
;; although we try to avoid CPS transformation on forms that do not
|
|
;; invoke `iter-yield'.
|
|
;;
|
|
|
|
;;; Code:
|
|
|
|
(require 'cl-lib)
|
|
|
|
(defvar cps--bindings nil)
|
|
(defvar cps--states nil)
|
|
(defvar cps--value-symbol nil)
|
|
(defvar cps--state-symbol nil)
|
|
(defvar cps--cleanup-table-symbol nil)
|
|
(defvar cps--cleanup-function nil)
|
|
|
|
(defmacro cps--gensym (fmt &rest args)
|
|
`(gensym (format ,fmt ,@args)))
|
|
|
|
(defvar cps--dynamic-wrappers '(identity)
|
|
"List of functions to apply to atomic forms.
|
|
These are transformer functions applied to atomic forms evaluated
|
|
in CPS context.")
|
|
|
|
(defconst cps-standard-special-forms
|
|
'(setq setq-default throw interactive)
|
|
"List of special forms treated just like ordinary function applications." )
|
|
|
|
(defun cps--trace-funcall (func &rest args)
|
|
(message "%S: args=%S" func args)
|
|
(let ((result (apply func args)))
|
|
(message "%S: result=%S" func result)
|
|
result))
|
|
|
|
(defun cps--trace (fmt &rest args)
|
|
(princ (apply #'format (concat fmt "\n") args)))
|
|
|
|
(defun cps--special-form-p (definition)
|
|
"Non-nil if and only if DEFINITION is a special form."
|
|
;; Copied from ad-special-form-p
|
|
(if (and (symbolp definition) (fboundp definition))
|
|
(setf definition (indirect-function definition)))
|
|
(and (subrp definition) (eq (cdr (subr-arity definition)) 'unevalled)))
|
|
|
|
(defmacro cps--define-unsupported (function)
|
|
`(defun ,(intern (format "cps--transform-%s" function))
|
|
(error "%s not supported in generators" ,function)))
|
|
|
|
(defmacro cps--with-value-wrapper (wrapper &rest body)
|
|
"Evaluate BODY with WRAPPER added to the stack of atomic-form wrappers.
|
|
WRAPPER is a function that takes an atomic form and returns a wrapped form.
|
|
|
|
Whenever we generate an atomic form (i.e., a form that can't
|
|
`iter-yield'), we first (before actually inserting that form in our
|
|
generated code) pass that form through all the transformer
|
|
functions. We use this facility to wrap forms that can transfer
|
|
control flow non-locally in goo that diverts this control flow to
|
|
the CPS state machinery."
|
|
(declare (indent 1))
|
|
`(let ((cps--dynamic-wrappers
|
|
(cons
|
|
,wrapper
|
|
cps--dynamic-wrappers)))
|
|
,@body))
|
|
|
|
(defun cps--make-dynamic-binding-wrapper (dynamic-var static-var)
|
|
(cl-assert lexical-binding)
|
|
(lambda (form)
|
|
`(let ((,dynamic-var ,static-var))
|
|
(unwind-protect ; Update the static shadow after evaluation is done
|
|
,form
|
|
(setf ,static-var ,dynamic-var)))))
|
|
|
|
(defmacro cps--with-dynamic-binding (dynamic-var static-var &rest body)
|
|
"Run BODY's atomic evaluations run with DYNAMIC-VAR bound to STATIC-VAR."
|
|
(declare (indent 2))
|
|
`(cps--with-value-wrapper
|
|
(cps--make-dynamic-binding-wrapper ,dynamic-var ,static-var)
|
|
,@body))
|
|
|
|
(defun cps--add-state (kind body)
|
|
"Create a new CPS state of KIND with BODY and return the state's name."
|
|
(declare (indent 1))
|
|
(let ((state (cps--gensym "cps-state-%s-" kind)))
|
|
(push (list state body cps--cleanup-function) cps--states)
|
|
(push state cps--bindings)
|
|
state))
|
|
|
|
(defun cps--add-binding (original-name)
|
|
(car (push (cps--gensym (format "cps-binding-%s-" original-name))
|
|
cps--bindings)))
|
|
|
|
(defun cps--find-special-form-handler (form)
|
|
(let* ((handler-name (format "cps--transform-%s" (car-safe form)))
|
|
(handler (intern-soft handler-name)))
|
|
(and (fboundp handler) handler)))
|
|
|
|
(defvar cps-inhibit-atomic-optimization nil
|
|
"When non-nil, always rewrite forms into CPS even when they don't yield.")
|
|
|
|
(defvar cps--yield-seen)
|
|
|
|
(defun cps--atomic-p (form)
|
|
"Return nil if FORM can yield, non-nil otherwise."
|
|
(and (not cps-inhibit-atomic-optimization)
|
|
(let* ((cps--yield-seen))
|
|
(ignore (macroexpand-all
|
|
`(cl-macrolet ((cps-internal-yield
|
|
(_val)
|
|
(setf cps--yield-seen t)))
|
|
,form)
|
|
macroexpand-all-environment))
|
|
(not cps--yield-seen))))
|
|
|
|
(defun cps--make-atomic-state (form next-state)
|
|
(let ((tform `(prog1 ,form (setf ,cps--state-symbol ,next-state))))
|
|
(cl-loop for wrapper in cps--dynamic-wrappers
|
|
do (setf tform (funcall wrapper tform)))
|
|
;; Bind cps--cleanup-function to nil here because the wrapper
|
|
;; function mechanism is responsible for cleanup here, not the
|
|
;; generic cleanup mechanism. If we didn't make this binding,
|
|
;; we'd run cleanup handlers twice on anything that made it out
|
|
;; to toplevel.
|
|
(let ((cps--cleanup-function nil))
|
|
(cps--add-state "atom"
|
|
`(setf ,cps--value-symbol ,tform)))))
|
|
|
|
(defun cps--transform-1 (form next-state)
|
|
(pcase form
|
|
|
|
;; If we're looking at an "atomic" form (i.e., one that does not
|
|
;; iter-yield), just evaluate the form as a whole instead of rewriting
|
|
;; it into CPS.
|
|
|
|
((guard (cps--atomic-p form))
|
|
(cps--make-atomic-state form next-state))
|
|
|
|
;; Process `and'.
|
|
|
|
('(and) ; (and) -> t
|
|
(cps--transform-1 t next-state))
|
|
(`(and ,condition) ; (and CONDITION) -> CONDITION
|
|
(cps--transform-1 condition next-state))
|
|
(`(and ,condition . ,rest)
|
|
;; Evaluate CONDITION; if it's true, go on to evaluate the rest
|
|
;; of the `and'.
|
|
(cps--transform-1
|
|
condition
|
|
(cps--add-state "and"
|
|
`(setf ,cps--state-symbol
|
|
(if ,cps--value-symbol
|
|
,(cps--transform-1 `(and ,@rest)
|
|
next-state)
|
|
,next-state)))))
|
|
|
|
;; Process `catch'.
|
|
|
|
(`(catch ,tag . ,body)
|
|
(let ((tag-binding (cps--add-binding "catch-tag")))
|
|
(cps--transform-1 tag
|
|
(cps--add-state "cps-update-tag"
|
|
`(setf ,tag-binding ,cps--value-symbol
|
|
,cps--state-symbol
|
|
,(cps--with-value-wrapper
|
|
(cps--make-catch-wrapper
|
|
tag-binding next-state)
|
|
(cps--transform-1 `(progn ,@body)
|
|
next-state)))))))
|
|
|
|
;; Process `cond': transform into `if' or `or' depending on the
|
|
;; precise kind of the condition we're looking at.
|
|
|
|
('(cond) ; (cond) -> nil
|
|
(cps--transform-1 nil next-state))
|
|
(`(cond (,condition) . ,rest)
|
|
(cps--transform-1 `(or ,condition (cond ,@rest))
|
|
next-state))
|
|
(`(cond (,condition . ,body) . ,rest)
|
|
(cps--transform-1 `(if ,condition
|
|
(progn ,@body)
|
|
(cond ,@rest))
|
|
next-state))
|
|
|
|
;; Process `condition-case': do the heavy lifting in a helper
|
|
;; function.
|
|
|
|
(`(condition-case ,var ,bodyform . ,handlers)
|
|
(cps--with-value-wrapper
|
|
(cps--make-condition-wrapper var next-state handlers)
|
|
(cps--transform-1 bodyform
|
|
next-state)))
|
|
|
|
;; Process `if'.
|
|
|
|
(`(if ,cond ,then . ,else)
|
|
(cps--transform-1 cond
|
|
(cps--add-state "if"
|
|
`(setf ,cps--state-symbol
|
|
(if ,cps--value-symbol
|
|
,(cps--transform-1 then
|
|
next-state)
|
|
,(cps--transform-1 `(progn ,@else)
|
|
next-state))))))
|
|
|
|
;; Process `progn' and `inline': they are identical except for the
|
|
;; name, which has some significance to the byte compiler.
|
|
|
|
('(inline) (cps--transform-1 nil next-state))
|
|
(`(inline ,form) (cps--transform-1 form next-state))
|
|
(`(inline ,form . ,rest)
|
|
(cps--transform-1 form
|
|
(cps--transform-1 `(inline ,@rest)
|
|
next-state)))
|
|
|
|
('(progn) (cps--transform-1 nil next-state))
|
|
(`(progn ,form) (cps--transform-1 form next-state))
|
|
(`(progn ,form . ,rest)
|
|
(cps--transform-1 form
|
|
(cps--transform-1 `(progn ,@rest)
|
|
next-state)))
|
|
|
|
(`(,(or 'let 'let*) () . ,body)
|
|
(cps--transform-1 `(progn ,@body) next-state))
|
|
|
|
;; Transform multi-variable `let' into `let*':
|
|
;; (let ((v1 e1) ... (vN eN)) BODY)
|
|
;; -> (let* ((t1 e1) ... (tN-1 eN-1) (vN eN) (v1 t1) (vN-1 tN-1)) BODY)
|
|
|
|
(`(let ,bindings . ,body)
|
|
(let* ((bindings (cl-loop for binding in bindings
|
|
collect (if (symbolp binding)
|
|
(list binding nil)
|
|
binding)))
|
|
(butlast-bindings (butlast bindings))
|
|
(temps (cl-loop for (var _value-form) in butlast-bindings
|
|
collect (cps--add-binding var))))
|
|
(cps--transform-1
|
|
`(let* ,(append
|
|
(cl-loop for (_var value-form) in butlast-bindings
|
|
for temp in temps
|
|
collect (list temp value-form))
|
|
(last bindings)
|
|
(cl-loop for (var _binding) in butlast-bindings
|
|
for temp in temps
|
|
collect (list var temp)))
|
|
,@body)
|
|
next-state)))
|
|
|
|
;; Process `let*' binding: process one binding at a time. Flatten
|
|
;; lexical bindings.
|
|
|
|
(`(let* (,binding . ,more-bindings) . ,body)
|
|
(let* ((var (if (symbolp binding) binding (car binding)))
|
|
(value-form (car (cdr-safe binding)))
|
|
(new-var (cps--add-binding var)))
|
|
|
|
(cps--transform-1
|
|
value-form
|
|
(cps--add-state "let*"
|
|
`(setf ,new-var ,cps--value-symbol
|
|
,cps--state-symbol
|
|
,(if (or (not lexical-binding) (special-variable-p var))
|
|
(cps--with-dynamic-binding var new-var
|
|
(cps--transform-1
|
|
`(let* ,more-bindings ,@body)
|
|
next-state))
|
|
(cps--transform-1
|
|
(cps--replace-variable-references
|
|
var new-var
|
|
`(let* ,more-bindings ,@body))
|
|
next-state)))))))
|
|
|
|
;; Process `or'.
|
|
|
|
('(or) (cps--transform-1 nil next-state))
|
|
(`(or ,condition) (cps--transform-1 condition next-state))
|
|
(`(or ,condition . ,rest)
|
|
(cps--transform-1
|
|
condition
|
|
(cps--add-state "or"
|
|
`(setf ,cps--state-symbol
|
|
(if ,cps--value-symbol
|
|
,next-state
|
|
,(cps--transform-1
|
|
`(or ,@rest) next-state))))))
|
|
|
|
;; Process `prog1'.
|
|
|
|
(`(prog1 ,first) (cps--transform-1 first next-state))
|
|
(`(prog1 ,first . ,body)
|
|
(cps--transform-1
|
|
first
|
|
(let ((temp-var-symbol (cps--add-binding "prog1-temp")))
|
|
(cps--add-state "prog1"
|
|
`(setf ,temp-var-symbol
|
|
,cps--value-symbol
|
|
,cps--state-symbol
|
|
,(cps--transform-1
|
|
`(progn ,@body)
|
|
(cps--add-state "prog1inner"
|
|
`(setf ,cps--value-symbol ,temp-var-symbol
|
|
,cps--state-symbol ,next-state))))))))
|
|
|
|
;; Process `unwind-protect': If we're inside an unwind-protect, we
|
|
;; have a block of code UNWINDFORMS which we would like to run
|
|
;; whenever control flows away from the main piece of code,
|
|
;; BODYFORM. We deal with the local control flow case by
|
|
;; generating BODYFORM such that it yields to a continuation that
|
|
;; executes UNWINDFORMS, which then yields to NEXT-STATE.
|
|
;;
|
|
;; Non-local control flow is trickier: we need to ensure that we
|
|
;; execute UNWINDFORMS even when control bypasses our normal
|
|
;; continuation. To make this guarantee, we wrap every external
|
|
;; application (i.e., every piece of elisp that can transfer
|
|
;; control non-locally) in an unwind-protect that runs UNWINDFORMS
|
|
;; before allowing the non-local control transfer to proceed.
|
|
;;
|
|
;; Unfortunately, because elisp lacks a mechanism for generically
|
|
;; capturing the reason for an arbitrary non-local control
|
|
;; transfer and restarting the transfer at a later point, we
|
|
;; cannot reify non-local transfers and cannot allow
|
|
;; continuation-passing code inside UNWINDFORMS.
|
|
|
|
(`(unwind-protect ,bodyform . ,unwindforms)
|
|
;; Signal the evaluator-generator that it needs to generate code
|
|
;; to handle cleanup forms.
|
|
(unless cps--cleanup-table-symbol
|
|
(setf cps--cleanup-table-symbol (cps--gensym "cps-cleanup-table-")))
|
|
(let* ((unwind-state
|
|
(cps--add-state
|
|
"unwind"
|
|
;; N.B. It's safe to just substitute unwindforms by
|
|
;; sexp-splicing: we've already replaced all variable
|
|
;; references inside it with lifted equivalents.
|
|
`(progn
|
|
,@unwindforms
|
|
(setf ,cps--state-symbol ,next-state))))
|
|
(old-cleanup cps--cleanup-function)
|
|
(cps--cleanup-function
|
|
(let ((cps--cleanup-function nil))
|
|
(cps--add-state "cleanup"
|
|
`(progn
|
|
,(when old-cleanup `(funcall ,old-cleanup))
|
|
,@unwindforms)))))
|
|
(cps--with-value-wrapper
|
|
(cps--make-unwind-wrapper unwindforms)
|
|
(cps--transform-1 bodyform unwind-state))))
|
|
|
|
;; Process `while'.
|
|
|
|
(`(while ,test . ,body)
|
|
;; Open-code state addition instead of using cps--add-state: we
|
|
;; need our states to be self-referential. (That's what makes the
|
|
;; state a loop.)
|
|
(let* ((loop-state
|
|
(cps--gensym "cps-state-while-"))
|
|
(eval-loop-condition-state
|
|
(cps--transform-1 test loop-state))
|
|
(loop-state-body
|
|
`(progn
|
|
(setf ,cps--state-symbol
|
|
(if ,cps--value-symbol
|
|
,(cps--transform-1
|
|
`(progn ,@body)
|
|
eval-loop-condition-state)
|
|
,next-state)))))
|
|
(push (list loop-state loop-state-body cps--cleanup-function)
|
|
cps--states)
|
|
(push loop-state cps--bindings)
|
|
eval-loop-condition-state))
|
|
|
|
;; Process various kinds of `quote'.
|
|
|
|
(`(quote ,arg) (cps--add-state "quote"
|
|
`(setf ,cps--value-symbol (quote ,arg)
|
|
,cps--state-symbol ,next-state)))
|
|
(`(function ,arg) (cps--add-state "function"
|
|
`(setf ,cps--value-symbol (function ,arg)
|
|
,cps--state-symbol ,next-state)))
|
|
|
|
;; Deal with `iter-yield'.
|
|
|
|
(`(cps-internal-yield ,value)
|
|
(cps--transform-1
|
|
value
|
|
(cps--add-state "iter-yield"
|
|
`(progn
|
|
(setf ,cps--state-symbol
|
|
,(if cps--cleanup-function
|
|
(cps--add-state "after-yield"
|
|
`(setf ,cps--state-symbol ,next-state))
|
|
next-state))
|
|
(throw 'cps--yield ,cps--value-symbol)))))
|
|
|
|
;; Catch any unhandled special forms.
|
|
|
|
((and `(,name . ,_)
|
|
(guard (cps--special-form-p name))
|
|
(guard (not (memq name cps-standard-special-forms))))
|
|
name ; Shut up byte compiler
|
|
(error "Special form %S incorrect or not supported" form))
|
|
|
|
;; Process regular function applications with nontrivial
|
|
;; parameters, converting them to applications of trivial
|
|
;; let-bound parameters.
|
|
|
|
((and `(,function . ,arguments)
|
|
(guard (not (cl-loop for argument in arguments
|
|
always (atom argument)))))
|
|
(let ((argument-symbols
|
|
(cl-loop for argument in arguments
|
|
collect (if (atom argument)
|
|
argument
|
|
(cps--gensym "cps-argument-")))))
|
|
|
|
(cps--transform-1
|
|
`(let* ,(cl-loop for argument in arguments
|
|
for argument-symbol in argument-symbols
|
|
unless (eq argument argument-symbol)
|
|
collect (list argument-symbol argument))
|
|
,(cons function argument-symbols))
|
|
next-state)))
|
|
|
|
;; Process everything else by just evaluating the form normally.
|
|
(_ (cps--make-atomic-state form next-state))))
|
|
|
|
(defun cps--make-catch-wrapper (tag-binding next-state)
|
|
(lambda (form)
|
|
(let ((normal-exit-symbol
|
|
(cps--gensym "cps-normal-exit-from-catch-")))
|
|
`(let (,normal-exit-symbol)
|
|
(prog1
|
|
(catch ,tag-binding
|
|
(prog1
|
|
,form
|
|
(setf ,normal-exit-symbol t)))
|
|
(unless ,normal-exit-symbol
|
|
(setf ,cps--state-symbol ,next-state)))))))
|
|
|
|
(defun cps--make-condition-wrapper (var next-state handlers)
|
|
;; Each handler is both one of the transformers with which we wrap
|
|
;; evaluated atomic forms and a state to which we jump when we
|
|
;; encounter the given error.
|
|
|
|
(let* ((error-symbol (cps--add-binding "condition-case-error"))
|
|
(lexical-error-symbol (cps--gensym "cps-lexical-error-"))
|
|
(processed-handlers
|
|
(cl-loop for (condition . body) in handlers
|
|
collect (cons condition
|
|
(cps--transform-1
|
|
(cps--replace-variable-references
|
|
var error-symbol
|
|
`(progn ,@body))
|
|
next-state)))))
|
|
|
|
(lambda (form)
|
|
`(condition-case
|
|
,lexical-error-symbol
|
|
,form
|
|
,@(cl-loop
|
|
for (condition . error-state) in processed-handlers
|
|
collect
|
|
`(,condition
|
|
(setf ,error-symbol
|
|
,lexical-error-symbol
|
|
,cps--state-symbol
|
|
,error-state)))))))
|
|
|
|
(defun cps--replace-variable-references (var new-var form)
|
|
"Replace all non-shadowed references to VAR with NEW-VAR in FORM.
|
|
This routine does not modify FORM. Instead, it returns a
|
|
modified copy."
|
|
(macroexpand-all
|
|
`(cl-symbol-macrolet ((,var ,new-var)) ,form)
|
|
macroexpand-all-environment))
|
|
|
|
(defun cps--make-unwind-wrapper (unwind-forms)
|
|
(cl-assert lexical-binding)
|
|
(lambda (form)
|
|
(let ((normal-exit-symbol
|
|
(cps--gensym "cps-normal-exit-from-unwind-")))
|
|
`(let (,normal-exit-symbol)
|
|
(unwind-protect
|
|
(prog1
|
|
,form
|
|
(setf ,normal-exit-symbol t))
|
|
(unless ,normal-exit-symbol
|
|
,@unwind-forms))))))
|
|
|
|
(define-error 'iter-end-of-sequence "Iteration terminated"
|
|
;; FIXME: This was not defined originally as an `error' condition, so
|
|
;; we reproduce this by passing itself as the parent, which avoids the
|
|
;; default `error' parent. Maybe it *should* be in the `error' category?
|
|
'iter-end-of-sequence)
|
|
|
|
(defun cps--make-close-iterator-form (terminal-state)
|
|
(if cps--cleanup-table-symbol
|
|
`(let ((cleanup (cdr (assq ,cps--state-symbol ,cps--cleanup-table-symbol))))
|
|
(setf ,cps--state-symbol ,terminal-state
|
|
,cps--value-symbol nil)
|
|
(when cleanup (funcall cleanup)))
|
|
`(setf ,cps--state-symbol ,terminal-state
|
|
,cps--value-symbol nil)))
|
|
|
|
(defun cps-generate-evaluator (body)
|
|
(let* (cps--states
|
|
cps--bindings
|
|
cps--cleanup-function
|
|
(cps--value-symbol (cps--gensym "cps-current-value-"))
|
|
(cps--state-symbol (cps--gensym "cps-current-state-"))
|
|
;; We make *cps-cleanup-table-symbol** non-nil when we notice
|
|
;; that we have cleanup processing to perform.
|
|
(cps--cleanup-table-symbol nil)
|
|
(terminal-state (cps--add-state "terminal"
|
|
`(signal 'iter-end-of-sequence
|
|
,cps--value-symbol)))
|
|
(initial-state (cps--transform-1
|
|
(macroexpand-all
|
|
`(cl-macrolet
|
|
((iter-yield (value)
|
|
`(cps-internal-yield ,value)))
|
|
,@body)
|
|
macroexpand-all-environment)
|
|
terminal-state))
|
|
(finalizer-symbol
|
|
(when cps--cleanup-table-symbol
|
|
(when cps--cleanup-table-symbol
|
|
(cps--gensym "cps-iterator-finalizer-")))))
|
|
`(let ,(append (list cps--state-symbol cps--value-symbol)
|
|
(when cps--cleanup-table-symbol
|
|
(list cps--cleanup-table-symbol))
|
|
(when finalizer-symbol
|
|
(list finalizer-symbol))
|
|
(nreverse cps--bindings))
|
|
;; Order state list so that cleanup states are always defined
|
|
;; before they're referenced.
|
|
,@(cl-loop for (state body cleanup) in (nreverse cps--states)
|
|
collect `(setf ,state (lambda () ,body))
|
|
when cleanup
|
|
do (cl-assert cps--cleanup-table-symbol)
|
|
and collect `(push (cons ,state ,cleanup) ,cps--cleanup-table-symbol))
|
|
(setf ,cps--state-symbol ,initial-state)
|
|
|
|
(let ((iterator
|
|
(lambda (op value)
|
|
(cond
|
|
,@(when finalizer-symbol
|
|
`(((eq op :stash-finalizer)
|
|
(setf ,finalizer-symbol value))
|
|
((eq op :get-finalizer)
|
|
,finalizer-symbol)))
|
|
((eq op :close)
|
|
,(cps--make-close-iterator-form terminal-state))
|
|
((eq op :next)
|
|
(setf ,cps--value-symbol value)
|
|
(let ((yielded nil))
|
|
(unwind-protect
|
|
(prog1
|
|
(catch 'cps--yield
|
|
(while t
|
|
(funcall ,cps--state-symbol)))
|
|
(setf yielded t))
|
|
(unless yielded
|
|
;; If we're exiting non-locally (error, quit,
|
|
;; etc.) close the iterator.
|
|
,(cps--make-close-iterator-form terminal-state)))))
|
|
(t (error "Unknown iterator operation %S" op))))))
|
|
,(when finalizer-symbol
|
|
'(funcall iterator
|
|
:stash-finalizer
|
|
(make-finalizer
|
|
(lambda ()
|
|
(iter-close iterator)))))
|
|
iterator))))
|
|
|
|
(defun iter-yield (_value)
|
|
"When used inside a generator, yield control to caller.
|
|
The caller of `iter-next' receives VALUE, and the next call to
|
|
`iter-next' resumes execution with the form immediately following this
|
|
`iter-yield' call."
|
|
(error "`iter-yield' used outside a generator"))
|
|
|
|
(defmacro iter-yield-from (value)
|
|
"When used inside a generator function, delegate to a sub-iterator.
|
|
The values that the sub-iterator yields are passed directly to
|
|
the caller, and values supplied to `iter-next' are sent to the
|
|
sub-iterator. `iter-yield-from' evaluates to the value that the
|
|
sub-iterator function returns via `iter-end-of-sequence'."
|
|
(let ((errsym (cps--gensym "yield-from-result"))
|
|
(valsym (cps--gensym "yield-from-value")))
|
|
`(let ((,valsym ,value))
|
|
(unwind-protect
|
|
(condition-case ,errsym
|
|
(let ((vs nil))
|
|
(while t
|
|
(setf vs (iter-yield (iter-next ,valsym vs)))))
|
|
(iter-end-of-sequence (cdr ,errsym)))
|
|
(iter-close ,valsym)))))
|
|
|
|
(defmacro iter-defun (name arglist &rest body)
|
|
"Create a generator NAME that accepts ARGLIST as its arguments.
|
|
When called as a function, NAME returns an iterator value that
|
|
encapsulates the state of a computation that produces a sequence
|
|
of values. Callers can retrieve each value using `iter-next'."
|
|
(declare (indent defun)
|
|
(debug (&define name lambda-list lambda-doc &rest sexp))
|
|
(doc-string 3))
|
|
(cl-assert lexical-binding)
|
|
(let* ((parsed-body (macroexp-parse-body body))
|
|
(declarations (car parsed-body))
|
|
(exps (cdr parsed-body)))
|
|
`(defun ,name ,arglist
|
|
,@declarations
|
|
,(cps-generate-evaluator exps))))
|
|
|
|
(defmacro iter-lambda (arglist &rest body)
|
|
"Return a lambda generator.
|
|
`iter-lambda' is to `iter-defun' as `lambda' is to `defun'."
|
|
(declare (indent defun)
|
|
(debug (&define lambda-list lambda-doc &rest sexp)))
|
|
(cl-assert lexical-binding)
|
|
(pcase-let* ((`(,declarations . ,exps) (macroexp-parse-body body)))
|
|
`(lambda ,arglist
|
|
,@declarations
|
|
,(cps-generate-evaluator exps))))
|
|
|
|
(defmacro iter-make (&rest body)
|
|
"Return a new iterator."
|
|
(declare (debug (&rest sexp)))
|
|
(cps-generate-evaluator body))
|
|
|
|
(defconst iter-empty (lambda (_op _val) (signal 'iter-end-of-sequence nil))
|
|
"Trivial iterator that always signals the end of sequence.")
|
|
|
|
(defun iter-next (iterator &optional yield-result)
|
|
"Extract a value from an iterator.
|
|
YIELD-RESULT becomes the return value of `iter-yield' in the
|
|
context of the generator.
|
|
|
|
This routine raises the `iter-end-of-sequence' condition if the
|
|
iterator cannot supply more values."
|
|
(funcall iterator :next yield-result))
|
|
|
|
(defun iter-close (iterator)
|
|
"Terminate an iterator early.
|
|
Run any `unwind-protect' handlers in scope at the point ITERATOR
|
|
is blocked."
|
|
(funcall iterator :close nil))
|
|
|
|
(cl-defmacro iter-do ((var iterator) &rest body)
|
|
"Loop over values from an iterator.
|
|
Evaluate BODY with VAR bound to each value from ITERATOR.
|
|
Return the value with which ITERATOR finished iteration."
|
|
(declare (indent 1)
|
|
(debug ((symbolp form) &rest sexp)))
|
|
(let ((done-symbol (cps--gensym "iter-do-iterator-done"))
|
|
(condition-symbol (cps--gensym "iter-do-condition"))
|
|
(it-symbol (cps--gensym "iter-do-iterator"))
|
|
(result-symbol (cps--gensym "iter-do-result")))
|
|
`(let (,result-symbol
|
|
(,done-symbol nil)
|
|
(,it-symbol ,iterator))
|
|
(while
|
|
(let ((,var
|
|
(condition-case ,condition-symbol
|
|
(iter-next ,it-symbol)
|
|
(iter-end-of-sequence
|
|
(setf ,result-symbol (cdr ,condition-symbol))
|
|
(setf ,done-symbol t)))))
|
|
(unless ,done-symbol
|
|
,@body
|
|
;; Loop until done-symbol is set.
|
|
t)))
|
|
,result-symbol)))
|
|
|
|
(defvar cl--loop-args)
|
|
|
|
(defmacro cps--advance-for (conscell)
|
|
;; See cps--handle-loop-for
|
|
`(condition-case nil
|
|
(progn
|
|
(setcar ,conscell (iter-next (cdr ,conscell)))
|
|
,conscell)
|
|
(iter-end-of-sequence
|
|
nil)))
|
|
|
|
(defmacro cps--initialize-for (iterator)
|
|
;; See cps--handle-loop-for
|
|
(let ((cs (cps--gensym "cps--loop-temp")))
|
|
`(let ((,cs (cons nil ,iterator)))
|
|
(cps--advance-for ,cs))))
|
|
|
|
(defun cps--handle-loop-for (var)
|
|
"Support `iter-by' in `loop'."
|
|
;; N.B. While the cl-loop-for-handler is a documented interface,
|
|
;; there's no documented way for cl-loop-for-handler callbacks to do
|
|
;; anything useful! Additionally, cl-loop currently lexbinds useful
|
|
;; internal variables, so our only option is to modify
|
|
;; cl--loop-args. If we substitute a general-purpose for-clause for
|
|
;; our iterating clause, however, we can't preserve the
|
|
;; parallel-versus-sequential `loop' semantics for for clauses ---
|
|
;; we need a terminating condition as well, which requires us to use
|
|
;; while, and inserting a while would break and-sequencing.
|
|
;;
|
|
;; To work around this problem, we actually use the "for var in LIST
|
|
;; by FUNCTION" syntax, creating a new fake list each time through
|
|
;; the loop, this "list" being a cons cell (val . it).
|
|
(let ((it-form (pop cl--loop-args)))
|
|
(setf cl--loop-args
|
|
(append
|
|
`(for ,var
|
|
in (cps--initialize-for ,it-form)
|
|
by 'cps--advance-for)
|
|
cl--loop-args))))
|
|
|
|
(put 'iter-by 'cl-loop-for-handler 'cps--handle-loop-for)
|
|
|
|
(eval-after-load 'elisp-mode
|
|
(lambda ()
|
|
(font-lock-add-keywords
|
|
'emacs-lisp-mode
|
|
'(("(\\(iter-defun\\)\\_>\\s *\\(\\(?:\\sw\\|\\s_\\)+\\)?"
|
|
(1 font-lock-keyword-face nil t)
|
|
(2 font-lock-function-name-face nil t))
|
|
("(\\(iter-\\(?:next\\|lambda\\|yield\\|yield-from\\)\\)\\_>"
|
|
(1 font-lock-keyword-face nil t))))))
|
|
|
|
(provide 'generator)
|
|
|
|
;;; generator.el ends here
|