[bug#30053] [PATCH 1/3] Improve appearance of tabular output.

[Steve Sprang <steve.sprang@gmail.com>]

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I noticed when listing installed or available packages that the output
is often pretty jumbled up because columns in each row have an
inconsistent width.

This series of patches adds a new procedure for printing tabular data
(pretty-print-table) and modifies the code for --list-installed,
--list-available, and --list-generations to utilize it.

-Steve

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From 09a6bbb1a8d5d2855cdee06b5937dc3e95b2f401 Mon Sep 17 00:00:00 2001
From: Steve Sprang <scs@stevesprang.com>
Date: Tue, 9 Jan 2018 14:00:11 -0800
Subject: [PATCH 1/3] utils: Add a procedure for pretty printing tabular data.

* guix/utils.scm (pretty-print-table): New procedure.
---
 guix/utils.scm | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/guix/utils.scm b/guix/utils.scm
index 92e45de61..cf1d88d21 100644
--- a/guix/utils.scm
+++ b/guix/utils.scm
@@ -46,7 +46,9 @@
   #:use-module ((ice-9 iconv) #:prefix iconv:)
   #:use-module (system foreign)
   #:re-export (memoize)         ; for backwards compatibility
-  #:export (strip-keyword-arguments
+  #:export (pretty-print-table
+
+            strip-keyword-arguments
             default-keyword-arguments
             substitute-keyword-arguments
             ensure-keyword-arguments
@@ -299,6 +301,24 @@ This procedure returns #t on success."
             #t))))))
 
 \f
+;;;
+;;; Prettified output.
+;;;
+
+(define (pretty-print-table rows)
+  "Print ROWS in neat columns.  All rows should be lists of strings and each
+row should have the same length."
+  (let* ((num-cols   (if (null? rows) 0 (length (car rows))))
+         (col-widths (fold (lambda (row maximums)
+                             (map max (map string-length row) maximums))
+                           ;; Initial max width is 0 for each column.
+                           (make-list num-cols 0)
+                           rows))
+         (col-fmts   (map (cut format #f "~~~da" <>) col-widths))
+         (fmt        (string-join col-fmts "~/")))
+    (map (cut format #t "~?~%" fmt <>) rows)))
+
+\f
 ;;;
 ;;; Keyword arguments.
 ;;;
-- 
2.15.1