[elpa] externals/dash 2626840 336/426: Add -fixfn

[Phillip Lord]

branch: externals/dash
commit 262684080296f0fbc4f35744f1e7543ed7f5afa0
Author: Matus Goljer <address@hidden>
Commit: Matus Goljer <address@hidden>

    Add -fixfn
---
 README.md          |   14 ++++++++++++++
 dash-functional.el |   13 +++++++++++++
 dash.el            |    1 +
 dev/examples.el    |    6 ++++++
 4 files changed, 34 insertions(+), 0 deletions(-)

diff --git a/README.md b/README.md
index 2b44acf..9567edf 100644
--- a/README.md
+++ b/README.md
@@ -250,6 +250,7 @@ These combinators require Emacs 24 for its lexical scope. 
So they are offered in
 * [-orfn](#-orfn-rest-preds) `(&rest preds)`
 * [-andfn](#-andfn-rest-preds) `(&rest preds)`
 * [-iteratefn](#-iteratefn-fn-n) `(fn n)`
+* [-fixfn](#-fixfn-fn) `(fn)`
 * [-prodfn](#-prodfn-rest-fns) `(&rest fns)`
 
 ## Anaphoric functions
@@ -1930,6 +1931,19 @@ This function satisfies the following law:
 (funcall (-iteratefn 'cdr 3) '(1 2 3 4 5)) ;; => '(4 5)
 ```
 
+#### -fixfn `(fn)`
+
+Return a function that computes the (least) fixpoint of `fn`.
+
+`fn` is a unary function, results are compared with `equal`.
+
+In types: (a -> a) -> a -> a.
+
+```cl
+(funcall (-fixfn 'cos) 0.7) ;; => 0.7390851332151607
+(funcall (-fixfn (lambda (x) (expt (+ x 10) 0.25))) 2.0) ;; => 
1.8555845286409378
+```
+
 #### -prodfn `(&rest fns)`
 
 Take a list of n functions and return a function that takes a
diff --git a/dash-functional.el b/dash-functional.el
index eb2484a..115f137 100644
--- a/dash-functional.el
+++ b/dash-functional.el
@@ -135,6 +135,19 @@ This function satisfies the following law:
   (funcall (-iteratefn fn n) init) = (-last-item (-iterate fn init (1+ n)))."
   (lambda (x) (--dotimes n (setq x (funcall fn x))) x))
 
+(defun -fixfn (fn)
+  "Return a function that computes the (least) fixpoint of FN.
+
+FN is a unary function, results are compared with `equal'.
+
+In types: (a -> a) -> a -> a."
+  (lambda (x)
+    (let ((re (funcall fn x)))
+      (while (not (equal x re))
+        (setq x re)
+        (setq re (funcall fn re)))
+      re)))
+
 (defun -prodfn (&rest fns)
   "Take a list of n functions and return a function that takes a
 list of length n, applying i-th function to i-th element of the
diff --git a/dash.el b/dash.el
index c90d3bf..9ba16ea 100644
--- a/dash.el
+++ b/dash.el
@@ -1780,6 +1780,7 @@ structure such as plist or alist."
                              "-orfn"
                              "-andfn"
                              "-iteratefn"
+                             "-fixfn"
                              "-prodfn"
                              ))
              (special-variables '(
diff --git a/dev/examples.el b/dev/examples.el
index 04fb8c3..9d8c9ea 100644
--- a/dev/examples.el
+++ b/dev/examples.el
@@ -801,6 +801,12 @@ new list."
              (equal (funcall (-iteratefn fn 5) init)
                     (-last-item (-iterate fn init (1+ 5)))))))
 
+    (defexamples -fixfn
+      ;; Find solution to cos(x) = x
+      (funcall (-fixfn 'cos) 0.7) => 0.7390851332151607
+      ;; Find solution to x^4 - x - 10 = 0
+      (funcall (-fixfn (lambda (x) (expt (+ x 10) 0.25))) 2.0) => 
1.8555845286409378)
+
     (defexamples -prodfn
       (funcall (-prodfn '1+ '1- 'int-to-string) '(1 2 3)) => '(2 1 "3")
       (-map (-prodfn '1+ '1-) '((1 2) (3 4) (5 6) (7 8))) => '((2 1) (4 3) (6 
5) (8 7))