Move stuff from calp/util to hnh/util.

This is the first (major) step in splitting the generally useful items
into its own library.

1 files changed, 40 insertions, 0 deletions

diff --git a/module/hnh/util/tree.scm b/module/hnh/util/tree.scm
new file mode 100644
index 00000000..6c4f765d
--- /dev/null
+++ b/module/hnh/util/tree.scm
@@ -0,0 +1,40 @@
+(define-module (hnh util tree)
+  #:use-module (srfi srfi-1)
+  #:use-module (hnh util)
+  #:export (make-tree left-subtree
+                      right-subtree
+                      length-of-longst-branch
+                      tree-map))
+
+;; Constructs a binary tree where each node's children is partitioned
+;; into a left and right branch using @var{pred?}.
+;; Has thee form @var{(node left-subtree right-subtree)}. A leaf has
+;; both it's children equal to @var{null}.
+(define (make-tree pred? lst)
+  (unless (null? lst)
+    (let* ((head tail (partition (lambda (el) (pred? (car lst) el))
+                                 (cdr lst))))
+      (list (car lst)
+            (make-tree pred? head)
+            (make-tree pred? tail)))))
+
+(define (left-subtree tree)
+  (list-ref tree 1))
+
+(define (right-subtree tree)
+  (list-ref tree 2))
+
+;; Length includes current node, so the length of a leaf is 1.
+(define (length-of-longst-branch tree)
+  (if (null? tree)
+      ;; Having the @var{1+} outside the @var{max} also works,
+      ;; but leads to events overlapping many other to be thinner.
+      ;; Having it inside makes all events as evenly wide as possible.
+      0 (max (1+ (length-of-longst-branch (left-subtree tree)))
+             (length-of-longst-branch (right-subtree tree)))))
+
+(define (tree-map proc tree)
+  (unless (null? tree)
+    (list (proc (car tree))
+          (tree-map proc (left-subtree tree))
+          (tree-map proc (right-subtree tree)))))