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-rw-r--r--hofs.lisp23
-rw-r--r--macros.lisp13
-rw-r--r--package.lisp5
3 files changed, 35 insertions, 6 deletions
diff --git a/hofs.lisp b/hofs.lisp
new file mode 100644
index 0000000..7eb1d51
--- /dev/null
+++ b/hofs.lisp
@@ -0,0 +1,23 @@
+;;; hofs.lisp -- higher-order functions
+
+(in-package :lambda-riffs)
+
+(defun labmda-if (pred then &optional (else (constantly nil)))
+ "Returns a function that applies PRED and conditionally executes
+THEN when PRED returned non-nil or otherwise executes ELSE. Each of
+PRED, THEN, and ELSE are assumed to accept the same arguments."
+ (lambda (&rest args)
+ (if (apply pred args)
+ (apply then args)
+ (apply else args))))
+
+(defun lambda-cond (&rest pairs)
+ "PAIRS is a list: PRED1 F1 PRED2 F2 ...
+ Returns a function that applies FN to the argumetns for the first N
+ such that PREDN returns non-nil. Each of the PREDN and FN are
+ assumed to accept the same arguments."
+ (lambda (&rest args)
+ (loop for (pred fn . more) on pairs by #'cddr
+ when (apply pred args)
+ return (apply fn args))))
+
diff --git a/macros.lisp b/macros.lisp
index fa93bc5..8cf528f 100644
--- a/macros.lisp
+++ b/macros.lisp
@@ -23,8 +23,7 @@
(declare (ignore subchar infix))
(let ((form1 (read stream)))
(if (symbolp form1)
- (list '$ (list (concatenate 'string "$"
- (symbol-name form1)))
+ (list '$ (list (concatenate 'string "$" (symbol-name form1)))
(read stream))
(list '$ () form1))))))
@@ -110,7 +109,11 @@ surrounding form.
`(lambda ,new-params ,expr)))
-
-
-
+(defmacro closure (&body body)
+ "Creates a lambda that accepts any number of arguments, all of which
+ are ignored."
+ (let ((args (gensym)))
+ `(lambda (&rest ,args)
+ (declare (ignorable ,args))
+ ,@body)))
diff --git a/package.lisp b/package.lisp
index dcadede..2db36f3 100644
--- a/package.lisp
+++ b/package.lisp
@@ -1,4 +1,7 @@
;;;; package.lisp
(defpackage #:lambda-riffs
- (:use #:cl))
+ (:use #:cl)
+ (:export #:closure
+ #:lambda-if
+ #:lambda-cond))