functions.lisp

   1 (in-package :alexandria)
   2
   3 ;;; To propagate return type and allow the compiler to eliminate the IF when
   4 ;;; it is known if the argument is function or not.
   5 (declaim (inline ensure-function))
   6
   7 (declaim (ftype (function (t) (values function &optional))
   8                 ensure-function))
   9 (defun ensure-function (function-designator)
  10   "Returns the function designated by FUNCTION-DESIGNATOR:
  11 if FUNCTION-DESIGNATOR is a function, it is returned, otherwise
  12 it must be a function name and its FDEFINITION is returned."
  13   (if (functionp function-designator)
  14       function-designator
  15       (fdefinition function-designator)))
  16
  17 (define-modify-macro ensure-functionf/1 () ensure-function)
  18
  19 (defmacro ensure-functionf (&rest places)
  20   "Multiple-place modify macro for ENSURE-FUNCTION: ensures that each of
  21 PLACES contains a function."
  22   `(progn ,@(mapcar (lambda (x) `(ensure-functionf/1 ,x)) places)))
  23
  24 (defun disjoin (predicate &rest more-predicates)
  25   "Returns a function that applies each of PREDICATE and MORE-PREDICATE
  26 functions in turn to its arguments, returning the primary value of the first
  27 predicate that returns true, without calling the remaining predicates.
  28 If none of the predicates returns true, NIL is returned."
  29   (declare (optimize (speed 3) (safety 1) (debug 1)))
  30   (let ((predicate (ensure-function predicate))
  31         (more-predicates (mapcar #'ensure-function more-predicates)))
  32     (lambda (&rest arguments)
  33       (or (apply predicate arguments)
  34           (some (lambda (p)
  35                   (declare (type function p))
  36                   (apply p arguments))
  37                 more-predicates)))))
  38
  39 (defun conjoin (predicate &rest more-predicates)
  40   "Returns a function that applies each of PREDICATE and MORE-PREDICATE
  41 functions in turn to its arguments, returning NIL if any of the predicates
  42 returns false, without calling the remaining predicates. If none of the
  43 predicates returns false, returns the primary value of the last predicate."
  44   (if (null more-predicates)
  45       predicate
  46       (lambda (&rest arguments)
  47         (and (apply predicate arguments)
  48              ;; Cannot simply use CL:EVERY because we want to return the
  49              ;; non-NIL value of the last predicate if all succeed.
  50              (do ((tail (cdr more-predicates) (cdr tail))
  51                   (head (car more-predicates) (car tail)))
  52                  ((not tail)
  53                   (apply head arguments))
  54                (unless (apply head arguments)
  55                  (return nil)))))))
  56
  57
  58 (defun compose (function &rest more-functions)
  59   "Returns a function composed of FUNCTION and MORE-FUNCTIONS that applies its
  60 arguments to to each in turn, starting from the rightmost of MORE-FUNCTIONS,
  61 and then calling the next one with the primary value of the last."
  62   (declare (optimize (speed 3) (safety 1) (debug 1)))
  63   (reduce (lambda (f g)
  64             (let ((f (ensure-function f))
  65                   (g (ensure-function g)))
  66               (lambda (&rest arguments)
  67                 (declare (dynamic-extent arguments))
  68                 (funcall f (apply g arguments)))))
  69           more-functions
  70           :initial-value function))
  71
  72 (define-compiler-macro compose (function &rest more-functions)
  73   (labels ((compose-1 (funs)
  74              (if (cdr funs)
  75                  `(funcall ,(car funs) ,(compose-1 (cdr funs)))
  76                  `(apply ,(car funs) arguments))))
  77     (let* ((args (cons function more-functions))
  78            (funs (make-gensym-list (length args) "COMPOSE")))
  79       `(let ,(loop for f in funs for arg in args
  80                    collect `(,f (ensure-function ,arg)))
  81          (declare (optimize (speed 3) (safety 1) (debug 1)))
  82          (lambda (&rest arguments)
  83            (declare (dynamic-extent arguments))
  84            ,(compose-1 funs))))))
  85
  86 (defun multiple-value-compose (function &rest more-functions)
  87     "Returns a function composed of FUNCTION and MORE-FUNCTIONS that applies
  88 its arguments to each in turn, starting from the rightmost of
  89 MORE-FUNCTIONS, and then calling the next one with all the return values of
  90 the last."
  91   (declare (optimize (speed 3) (safety 1) (debug 1)))
  92   (reduce (lambda (f g)
  93             (let ((f (ensure-function f))
  94                   (g (ensure-function g)))
  95               (lambda (&rest arguments)
  96                 (declare (dynamic-extent arguments))
  97                 (multiple-value-call f (apply g arguments)))))
  98           more-functions
  99           :initial-value function))
 100
 101 (define-compiler-macro multiple-value-compose (function &rest more-functions)
 102   (labels ((compose-1 (funs)
 103              (if (cdr funs)
 104                  `(multiple-value-call ,(car funs) ,(compose-1 (cdr funs)))
 105                  `(apply ,(car funs) arguments))))
 106     (let* ((args (cons function more-functions))
 107            (funs (make-gensym-list (length args) "MV-COMPOSE")))
 108       `(let ,(mapcar #'list funs args)
 109          (declare (optimize (speed 3) (safety 1) (debug 1)))
 110          (lambda (&rest arguments)
 111            (declare (dynamic-extent arguments))
 112            ,(compose-1 funs))))))
 113
 114 (defun curry (function &rest arguments)
 115   "Returns a function that applies ARGUMENTS and the arguments
 116 it is called with to FUNCTION."
 117   (declare (optimize (speed 3) (safety 1) (debug 1)))
 118   (let ((fn (ensure-function function)))
 119     (lambda (&rest more)
 120       (declare (dynamic-extent more))
 121       ;; Using M-V-C we don't need to append the arguments.
 122       (multiple-value-call fn (values-list arguments) (values-list more)))))
 123
 124 (define-compiler-macro curry (function &rest arguments)
 125   (let ((curries (make-gensym-list (length arguments) "CURRY"))
 126         (fun (gensym "FUN")))
 127     `(let ((,fun (ensure-function ,function))
 128            ,@(mapcar #'list curries arguments))
 129        (declare (optimize (speed 3) (safety 1) (debug 1)))
 130        (lambda (&rest more)
 131          (apply ,fun ,@curries more)))))
 132
 133 (defun rcurry (function &rest arguments)
 134   "Returns a function that applies the arguments it is called
 135 with and ARGUMENTS to FUNCTION."
 136   (declare (optimize (speed 3) (safety 1) (debug 1)))
 137   (let ((fn (ensure-function function)))
 138     (lambda (&rest more)
 139       (declare (dynamic-extent more))
 140       (multiple-value-call fn (values-list more) (values-list arguments)))))
 141
 142 (defmacro named-lambda (name lambda-list &body body)
 143   "Expands into a lambda-expression within whose BODY NAME denotes the
 144 corresponding function."
 145   `(labels ((,name ,lambda-list ,@body))
 146      #',name))