infix: add quadratic-roots test

* tests/012/infix.tl (quadractic-roots): New function.
Add couple of tests.

* txr.1: Add quadratic-roots as example to ifx macro.

2 files changed, 24 insertions, 0 deletions

diff --git a/tests/012/infix.tl b/tests/012/infix.tl
index c619db18..79767f31 100644
--- a/tests/012/infix.tl
+++ b/tests/012/infix.tl
@@ -65,3 +65,13 @@
   (x ** a[i][j][k] ++) (expt x (pinc [[[a i] j] k]))
   (x ** -- a[i][j][k]) (expt x (dec [[[a i] j] k]))
   (x ** -- a[i + y][j ++][-- k]) (expt x (dec [[[a i + y] j ++] -- k])))
+
+(ifx
+  (defun quadratic-roots (a b c)
+    (let ((d (sqrt b * b - 4 * a * c)))
+      (list ((- b + d) / 2 * a)
+            ((- b - d) / 2 * a)))))
+
+(mtest
+  (quadratic-roots 1 0 -4) (2.0 -2.0)
+  (quadratic-roots 1 2 1) (-1.0 -1.0))
diff --git a/txr.1 b/txr.1
index b2b01fb9..2e2597ab 100644
--- a/txr.1
+++ b/txr.1
@@ -54327,6 +54327,20 @@ continues to apply, infix subexpressions produced by
 .code parse-infix
 are recursively detected and expanded.
 
+.TP* Example
+
+Calculate the roots of a quadratic formula, when real:
+
+.verb
+  (ifx
+    (defun quadratic-roots (a b c)
+      (let ((d (sqrt b * b - 4 * a * c)))
+        (list ((- b + d) / 2 * a)
+              ((- b - d) / 2 * a)))))
+
+  (quadratic-roots 1 0 -4)  ->  (2.0 -2.0)
+  (quadratic-roots 1 2 1)  ->  (-1.0 -1.0)
+.brev
 .SS* Enumerated Constants
 
 The enumerated constants module provides ways for defining