-;;;--------------------------------------------------------------------------
-;;; Some simple yet useful control structures.
-
-(defmacro nlet (name binds &body body)
- "Scheme's named let."
- (multiple-value-bind (vars vals)
- (loop for bind in binds
- for (var val) = (pairify bind nil)
- collect var into vars
- collect val into vals
- finally (return (values vars vals)))
- `(labels ((,name ,vars
- ,@body))
- (,name ,@vals))))
-
-(defmacro while (cond &body body)
- "If COND is false, evaluate to nil; otherwise evaluate BODY and try again."
- `(loop (unless ,cond (return)) (progn ,@body)))
-
-(defmacro until (cond &body body)
- "If COND is true, evaluate to nil; otherwise evaluate BODY and try again."
- `(loop (when ,cond (return)) (progn ,@body)))
-
-(compile-time-defun do-case2-like (kind vform clauses)
- "Helper function for `case2' and `ecase2'."
- (with-gensyms (scrutinee argument)
- `(multiple-value-bind (,scrutinee ,argument) ,vform
- (declare (ignorable ,argument))
- (,kind ,scrutinee
- ,@(mapcar (lambda (clause)
- (destructuring-bind
- (cases (&optional varx vary) &rest forms)
- clause
- `(,cases
- ,@(if varx
- (list `(let ((,(or vary varx) ,argument)
- ,@(and vary
- `((,varx ,scrutinee))))
- ,@forms))
- forms))))
- clauses)))))
-
-(defmacro case2 (vform &body clauses)
- "VFORM is a form which evaluates to two values, SCRUTINEE and ARGUMENT.
- The CLAUSES have the form (CASES ([[SCRUVAR] ARGVAR]) FORMS...), where a
- standard `case' clause has the form (CASES FORMS...). The `case2' form
- evaluates the VFORM, and compares the SCRUTINEE to the various CASES, in
- order, just like `case'. If there is a match, then the corresponding
- FORMs are evaluated with ARGVAR bound to the ARGUMENT and SCRUVAR bound to
- the SCRUTINEE (where specified). Note the bizarre defaulting behaviour:
- ARGVAR is less optional than SCRUVAR."
- (do-case2-like 'case vform clauses))
-
-(defmacro ecase2 (vform &body clauses)
- "Like `case2', but signals an error if no clause matches the SCRUTINEE."
- (do-case2-like 'ecase vform clauses))
-
-(defmacro setf-default (&rest specs &environment env)
- "Like setf, but only sets places which are currently nil.
-
- The arguments are an alternating list of PLACEs and DEFAULTs. If a PLACE
- is nil, the DEFAULT is evaluated and stored in the PLACE; otherwise the
- default is /not/ stored. The result is the (new) value of the last
- PLACE."
- (labels ((doit (specs)
- (cond ((null specs) nil)
- ((null (cdr specs))
- (error "Odd number of arguments for SETF-DEFAULT."))
- (t
- (let ((place (car specs))
- (default (cadr specs))
- (rest (cddr specs)))
- (multiple-value-bind
- (vars vals store-vals writer reader)
- (get-setf-expansion place env)
- `(let* ,(mapcar #'list vars vals)
- (or ,reader
- (multiple-value-bind ,store-vals ,default
- ,writer))
- ,@(and rest (list (doit rest))))))))))
- (doit specs)))
-