085446742970

--- a/README.markdown	Fri Feb 22 19:33:13 2019 -0500
+++ b/README.markdown	Sat Feb 23 12:48:24 2019 -0500
@@ -195,3 +195,29 @@
 Did some more Rosalind problems.  I'm up to 33 or so now.  These were fairly
 straightforward, but there are some other trickier ones I need to think about
 more.
+
+## 2019-02-23
+
+Did another Rosalind problem.  Spent some time dicking around with `format` to
+try to figure out how to do the equivalent of the following:
+
+    (format nil "~{~,VF~^ ~}" precision floats)
+
+The intent is to print all the floats with the given precision.  This doesn't
+work, because the `V` is inside the `~{~}` directive, and so `format` expects
+two list items per iteration.  Options:
+
+1. Generate a control string at runtime with a separate `format` (gross).
+2. Define `print-float` to be a formatting function that uses a dynamic variable
+   and use`~/print-float/` in the control string (awkward).
+3. Interleave the precision in the list (wasteful).
+4. Do something horrible.
+
+I went with option 4:
+
+    (defun float-string (float-or-floats &optional (precision 3))
+      (with-output-to-string (s)
+        (loop :for (float . more) :on (ensure-list float-or-floats)
+              :do (format s "~,VF~:[~; ~]" precision float more))))
+
+