Add: hofs and closure

1 files changed, 23 insertions, 0 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))))
+