Add utils module.

* haunt/utils.scm: New file.
* Makefile.am (SOURCES): Add it.

haunt/utils.scm

@@ -0,0 +1,58 @@
+;;; Haunt --- Static site generator for GNU Guile
+;;; Copyright © 2015 David Thompson <davet@gnu.org>
+;;;
+;;; This file is part of Haunt.
+;;;
+;;; Haunt is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; Haunt is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Haunt.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+;; Miscellaneous utility procedures.
+;;
+;;; Code:
+
+(define-module (haunt utils)
+  #:use-module (ice-9 ftw)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:export (flatten
+            flat-map
+            string-split-at))
+
+(define* (flatten lst #:optional depth)
+  "Return a list that recursively concatenates the sub-lists of LST,
+up to DEPTH levels deep.  When DEPTH is #f, the entire tree is
+flattened."
+  (if (and (number? depth) (zero? depth))
+      lst
+      (fold-right (match-lambda*
+                   (((sub-list ...) memo)
+                    (append (flatten sub-list (and depth (1- depth)))
+                            memo))
+                   ((elem memo)
+                    (cons elem memo)))
+                  '()
+                  lst)))
+
+(define (flat-map proc . lsts)
+  (flatten (apply map proc lsts) 1))
+
+(define (string-split-at str char-pred)
+  (let ((i (string-index str char-pred)))
+    (if i
+        (list (string-take str i)
+              (string-drop str (1+ i)))
+        (list str))))
+