Add unicode border style.

table.scm

@@ -28,6 +28,8 @@
 (module
  table
  (
+  *table-border-style*
+  table->string
   table-tests!
   )
 
@@ -39,6 +41,9 @@
 	 ansi
 	 testing)
 
+ ;; Default table border style to use if not explicitly specified.
+ (define *table-border-style* (make-parameter 'ascii))
+
  ;; Returns a list of strings representing the rows in the original
  ;; string.
  (define (string->rows str)
@@ -156,10 +161,16 @@
 
  ;; Table border styles in visual form
  (define table-borders-lookup-source
-   '((ascii "/~,\\"
-	    "| ||"
-	    ">-+<"
-	    "'~^`")))
+   '((ascii
+      "/~,\\"
+      "| ||"
+      ">-+<"
+      "'~^`")
+     (unicode
+      "┌─┬┐"
+      "│ ││"
+      "├─┼┤"
+      "└─┴┘")))
 
  ;; Compiled table borders for rendering
  (define table-borders-lookup