ui: Add support for colorization.

* guix/ui.scm (ansi-color-tables): New variable.
(color, colorize-string): New procedures.

Signed-off-by: Ricardo Wurmus <rekado@elephly.net>

guix/ui.scm

@@ -10,6 +10,8 @@
 ;;; Copyright © 2016 Roel Janssen <roel@gnu.org>
 ;;; Copyright © 2016 Benz Schenk <benz.schenk@uzh.ch>
 ;;; Copyright © 2018 Kyle Meyer <kyle@kyleam.com>
+;;; Copyright © 2013, 2014 Free Software Foundation, Inc.
+;;; Copyright © 2018 Sahithi Yarlagadda <sahi@swecha.net>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -115,7 +117,8 @@
             guix-warning-port
             warning
             info
-            guix-main))
+            guix-main
+            colorize-string))
 
 ;;; Commentary:
 ;;;
@@ -1622,4 +1625,54 @@ and signal handling has already been set up."
   (initialize-guix)
   (apply run-guix args))
 
+(define color-table
+  `((CLEAR       .   "0")
+    (RESET       .   "0")
+    (BOLD        .   "1")
+    (DARK        .   "2")
+    (UNDERLINE   .   "4")
+    (UNDERSCORE  .   "4")
+    (BLINK       .   "5")
+    (REVERSE     .   "6")
+    (CONCEALED   .   "8")
+    (BLACK       .  "30")
+    (RED         .  "31")
+    (GREEN       .  "32")
+    (YELLOW      .  "33")
+    (BLUE        .  "34")
+    (MAGENTA     .  "35")
+    (CYAN        .  "36")
+    (WHITE       .  "37")
+    (ON-BLACK    .  "40")
+    (ON-RED      .  "41")
+    (ON-GREEN    .  "42")
+    (ON-YELLOW   .  "43")
+    (ON-BLUE     .  "44")
+    (ON-MAGENTA  .  "45")
+    (ON-CYAN     .  "46")
+    (ON-WHITE    .  "47")))
+
+(define (color . lst)
+  "Return a string containing the ANSI escape sequence for producing the
+requested set of attributes in LST.  Unknown attributes are ignored."
+  (let ((color-list
+         (remove not
+                 (map (lambda (color) (assq-ref color-table color))
+                      lst))))
+    (if (null? color-list)
+        ""
+        (string-append
+         (string #\esc #\[)
+         (string-join color-list ";" 'infix)
+         "m"))))
+
+(define (colorize-string str . color-list)
+  "Return a copy of STR colorized using ANSI escape sequences according to the
+attributes STR.  At the end of the returned string, the color attributes will
+be reset such that subsequent output will not have any colors in effect."
+  (string-append
+   (apply color color-list)
+   str
+   (color 'RESET)))
+
 ;;; ui.scm ends here