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Diffstat (limited to 'macros.lisp')
| -rw-r--r-- | macros.lisp | 370 |
1 files changed, 370 insertions, 0 deletions
diff --git a/macros.lisp b/macros.lisp new file mode 100644 index 0000000000..4364ad63b8 --- /dev/null +++ b/macros.lisp @@ -0,0 +1,370 @@ +(in-package :alexandria) + +(defmacro with-gensyms (names &body forms) + "Binds a set of variables to gensyms and evaluates the implicit progn FORMS. + +Each element within NAMES is either a symbol SYMBOL or a pair (SYMBOL +STRING-DESIGNATOR). Bare symbols are equivalent to the pair (SYMBOL SYMBOL). + +Each pair (SYMBOL STRING-DESIGNATOR) specifies that the variable named by SYMBOL +should be bound to a symbol constructed using GENSYM with the string designated +by STRING-DESIGNATOR being its first argument." + `(let ,(mapcar (lambda (name) + (multiple-value-bind (symbol string) + (etypecase name + (symbol + (values name (symbol-name name))) + ((cons symbol (cons string-designator null)) + (values (first name) (string (second name))))) + `(,symbol (gensym ,string)))) + names) + ,@forms)) + +(defmacro with-unique-names (names &body forms) + "Alias for WITH-GENSYMS." + `(with-gensyms ,names ,@forms)) + +(defmacro once-only (specs &body forms) + "Constructs code whose primary goal is to help automate the handling of +multiple evaluation within macros. Multiple evaluation is handled by introducing +intermediate variables, in order to reuse the result of an expression. + +The returned value is a list of the form + + (let ((<gensym-1> <expr-1>) + ... + (<gensym-n> <expr-n>)) + <res>) + +where GENSYM-1, ..., GENSYM-N are the intermediate variables introduced in order +to evaluate EXPR-1, ..., EXPR-N once, only. RES is code that is the result of +evaluating the implicit progn FORMS within a special context determined by +SPECS. RES should make use of (reference) the intermediate variables. + +Each element within SPECS is either a symbol SYMBOL or a pair (SYMBOL INITFORM). +Bare symbols are equivalent to the pair (SYMBOL SYMBOL). + +Each pair (SYMBOL INITFORM) specifies a single intermediate variable: + +- INITFORM is an expression evaluated to produce EXPR-i + +- SYMBOL is the name of the variable that will be bound around FORMS to the + corresponding gensym GENSYM-i, in order for FORMS to generate RES that + references the intermediate variable + +The evaluation of INITFORMs and binding of SYMBOLs resembles LET. INITFORMs of +all the pairs are evaluated before binding SYMBOLs and evaluating FORMS. + +Example: + + The following expression + + (let ((x '(incf y))) + (once-only (x) + `(cons ,x ,x))) + + ;;; => + ;;; (let ((#1=#:X123 (incf y))) + ;;; (cons #1# #1#)) + + could be used within a macro to avoid multiple evaluation like so + + (defmacro cons1 (x) + (once-only (x) + `(cons ,x ,x))) + + (let ((y 0)) + (cons1 (incf y))) + + ;;; => (1 . 1) + +Example: + + The following expression demonstrates the usage of the INITFORM field + + (let ((expr '(incf y))) + (once-only ((var `(1+ ,expr))) + `(list ',expr ,var ,var))) + + ;;; => + ;;; (let ((#1=#:VAR123 (1+ (incf y)))) + ;;; (list '(incf y) #1# #1)) + + which could be used like so + + (defmacro print-succ-twice (expr) + (once-only ((var `(1+ ,expr))) + `(format t \"Expr: ~s, Once: ~s, Twice: ~s~%\" ',expr ,var ,var))) + + (let ((y 10)) + (print-succ-twice (incf y))) + + ;;; >> + ;;; Expr: (INCF Y), Once: 12, Twice: 12" + (let ((gensyms (make-gensym-list (length specs) "ONCE-ONLY")) + (names-and-forms (mapcar (lambda (spec) + (etypecase spec + (list + (destructuring-bind (name form) spec + (cons name form))) + (symbol + (cons spec spec)))) + specs))) + ;; bind in user-macro + `(let ,(mapcar (lambda (g n) (list g `(gensym ,(string (car n))))) + gensyms names-and-forms) + ;; bind in final expansion + `(let (,,@(mapcar (lambda (g n) + ``(,,g ,,(cdr n))) + gensyms names-and-forms)) + ;; bind in user-macro + ,(let ,(mapcar (lambda (n g) (list (car n) g)) + names-and-forms gensyms) + ,@forms))))) + +(defun parse-body (body &key documentation whole) + "Parses BODY into (values remaining-forms declarations doc-string). +Documentation strings are recognized only if DOCUMENTATION is true. +Syntax errors in body are signalled and WHOLE is used in the signal +arguments when given." + (let ((doc nil) + (decls nil) + (current nil)) + (tagbody + :declarations + (setf current (car body)) + (when (and documentation (stringp current) (cdr body)) + (if doc + (error "Too many documentation strings in ~S." (or whole body)) + (setf doc (pop body))) + (go :declarations)) + (when (and (listp current) (eql (first current) 'declare)) + (push (pop body) decls) + (go :declarations))) + (values body (nreverse decls) doc))) + +(defun parse-ordinary-lambda-list (lambda-list &key (normalize t) + allow-specializers + (normalize-optional normalize) + (normalize-keyword normalize) + (normalize-auxilary normalize)) + "Parses an ordinary lambda-list, returning as multiple values: + +1. Required parameters. + +2. Optional parameter specifications, normalized into form: + + (name init suppliedp) + +3. Name of the rest parameter, or NIL. + +4. Keyword parameter specifications, normalized into form: + + ((keyword-name name) init suppliedp) + +5. Boolean indicating &ALLOW-OTHER-KEYS presence. + +6. &AUX parameter specifications, normalized into form + + (name init). + +7. Existence of &KEY in the lambda-list. + +Signals a PROGRAM-ERROR is the lambda-list is malformed." + (let ((state :required) + (allow-other-keys nil) + (auxp nil) + (required nil) + (optional nil) + (rest nil) + (keys nil) + (keyp nil) + (aux nil)) + (labels ((fail (elt) + (simple-program-error "Misplaced ~S in ordinary lambda-list:~% ~S" + elt lambda-list)) + (check-variable (elt what &optional (allow-specializers allow-specializers)) + (unless (and (or (symbolp elt) + (and allow-specializers + (consp elt) (= 2 (length elt)) (symbolp (first elt)))) + (not (constantp elt))) + (simple-program-error "Invalid ~A ~S in ordinary lambda-list:~% ~S" + what elt lambda-list))) + (check-spec (spec what) + (destructuring-bind (init suppliedp) spec + (declare (ignore init)) + (check-variable suppliedp what nil)))) + (dolist (elt lambda-list) + (case elt + (&optional + (if (eq state :required) + (setf state elt) + (fail elt))) + (&rest + (if (member state '(:required &optional)) + (setf state elt) + (fail elt))) + (&key + (if (member state '(:required &optional :after-rest)) + (setf state elt) + (fail elt)) + (setf keyp t)) + (&allow-other-keys + (if (eq state '&key) + (setf allow-other-keys t + state elt) + (fail elt))) + (&aux + (cond ((eq state '&rest) + (fail elt)) + (auxp + (simple-program-error "Multiple ~S in ordinary lambda-list:~% ~S" + elt lambda-list)) + (t + (setf auxp t + state elt)) + )) + (otherwise + (when (member elt '#.(set-difference lambda-list-keywords + '(&optional &rest &key &allow-other-keys &aux))) + (simple-program-error + "Bad lambda-list keyword ~S in ordinary lambda-list:~% ~S" + elt lambda-list)) + (case state + (:required + (check-variable elt "required parameter") + (push elt required)) + (&optional + (cond ((consp elt) + (destructuring-bind (name &rest tail) elt + (check-variable name "optional parameter") + (cond ((cdr tail) + (check-spec tail "optional-supplied-p parameter")) + ((and normalize-optional tail) + (setf elt (append elt '(nil)))) + (normalize-optional + (setf elt (append elt '(nil nil))))))) + (t + (check-variable elt "optional parameter") + (when normalize-optional + (setf elt (cons elt '(nil nil)))))) + (push (ensure-list elt) optional)) + (&rest + (check-variable elt "rest parameter") + (setf rest elt + state :after-rest)) + (&key + (cond ((consp elt) + (destructuring-bind (var-or-kv &rest tail) elt + (cond ((consp var-or-kv) + (destructuring-bind (keyword var) var-or-kv + (unless (symbolp keyword) + (simple-program-error "Invalid keyword name ~S in ordinary ~ + lambda-list:~% ~S" + keyword lambda-list)) + (check-variable var "keyword parameter"))) + (t + (check-variable var-or-kv "keyword parameter") + (when normalize-keyword + (setf var-or-kv (list (make-keyword var-or-kv) var-or-kv))))) + (cond ((cdr tail) + (check-spec tail "keyword-supplied-p parameter")) + ((and normalize-keyword tail) + (setf tail (append tail '(nil)))) + (normalize-keyword + (setf tail '(nil nil)))) + (setf elt (cons var-or-kv tail)))) + (t + (check-variable elt "keyword parameter") + (setf elt (if normalize-keyword + (list (list (make-keyword elt) elt) nil nil) + elt)))) + (push elt keys)) + (&aux + (if (consp elt) + (destructuring-bind (var &optional init) elt + (declare (ignore init)) + (check-variable var "&aux parameter")) + (progn + (check-variable elt "&aux parameter") + (setf elt (list* elt (when normalize-auxilary + '(nil)))))) + (push elt aux)) + (t + (simple-program-error "Invalid ordinary lambda-list:~% ~S" lambda-list))))))) + (values (nreverse required) (nreverse optional) rest (nreverse keys) + allow-other-keys (nreverse aux) keyp))) + +;;;; DESTRUCTURING-*CASE + +(defun expand-destructuring-case (key clauses case) + (once-only (key) + `(if (typep ,key 'cons) + (,case (car ,key) + ,@(mapcar (lambda (clause) + (destructuring-bind ((keys . lambda-list) &body body) clause + `(,keys + (destructuring-bind ,lambda-list (cdr ,key) + ,@body)))) + clauses)) + (error "Invalid key to DESTRUCTURING-~S: ~S" ',case ,key)))) + +(defmacro destructuring-case (keyform &body clauses) + "DESTRUCTURING-CASE, -CCASE, and -ECASE are a combination of CASE and DESTRUCTURING-BIND. +KEYFORM must evaluate to a CONS. + +Clauses are of the form: + + ((CASE-KEYS . DESTRUCTURING-LAMBDA-LIST) FORM*) + +The clause whose CASE-KEYS matches CAR of KEY, as if by CASE, CCASE, or ECASE, +is selected, and FORMs are then executed with CDR of KEY is destructured and +bound by the DESTRUCTURING-LAMBDA-LIST. + +Example: + + (defun dcase (x) + (destructuring-case x + ((:foo a b) + (format nil \"foo: ~S, ~S\" a b)) + ((:bar &key a b) + (format nil \"bar: ~S, ~S\" a b)) + (((:alt1 :alt2) a) + (format nil \"alt: ~S\" a)) + ((t &rest rest) + (format nil \"unknown: ~S\" rest)))) + + (dcase (list :foo 1 2)) ; => \"foo: 1, 2\" + (dcase (list :bar :a 1 :b 2)) ; => \"bar: 1, 2\" + (dcase (list :alt1 1)) ; => \"alt: 1\" + (dcase (list :alt2 2)) ; => \"alt: 2\" + (dcase (list :quux 1 2 3)) ; => \"unknown: 1, 2, 3\" + + (defun decase (x) + (destructuring-case x + ((:foo a b) + (format nil \"foo: ~S, ~S\" a b)) + ((:bar &key a b) + (format nil \"bar: ~S, ~S\" a b)) + (((:alt1 :alt2) a) + (format nil \"alt: ~S\" a)))) + + (decase (list :foo 1 2)) ; => \"foo: 1, 2\" + (decase (list :bar :a 1 :b 2)) ; => \"bar: 1, 2\" + (decase (list :alt1 1)) ; => \"alt: 1\" + (decase (list :alt2 2)) ; => \"alt: 2\" + (decase (list :quux 1 2 3)) ; =| error +" + (expand-destructuring-case keyform clauses 'case)) + +(defmacro destructuring-ccase (keyform &body clauses) + (expand-destructuring-case keyform clauses 'ccase)) + +(defmacro destructuring-ecase (keyform &body clauses) + (expand-destructuring-case keyform clauses 'ecase)) + +(dolist (name '(destructuring-ccase destructuring-ecase)) + (setf (documentation name 'function) (documentation 'destructuring-case 'function))) + + + |