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copied!<pre><code>timesToUnixTimes :: [String] -> [UTCTime] </code></pre> <p>As ja points out, this is not a simple <code>map</code>. But the final step of converting a <code>[Integer]</code> to a <code>[UTCTime]</code> is a <code>map</code>:</p> <pre><code>timesToUnixTimes (s : ss) = map psUTC (i : is) where </code></pre> <p>The first element of the input list, <code>s</code>, had better be a unixtime:</p> <pre><code> i = read (tail s) :: Integer </code></pre> <p>Subsequent elements, <code>ss</code>, may be either, so the decoding function needs access to the previous element of the output list:</p> <pre><code> is = zipWith timeToInteger ss (i : is) </code></pre> <p>Writing <code>timeToInteger :: String -> Integer -> Integer</code> is left as an exercise.</p> <p>Two points from this:</p> <ol> <li><p>You can think of <code>zipWith</code> as mapping a function over two lists at a time (similarly, <code>zipWith3</code> maps a function over three lists at a time, <code>zipWith4</code> maps over four lists at a time, etc; there isn't a function called <code>zipWith1</code> because it's called <code>map</code>).</p></li> <li><p><code>is</code> appears in its own definition. This works thanks to <s>laziness</s> non-strictness.</p> <ol> <li>The first element of <code>is</code> depends on the first element of <code>ss</code> and on <code>i</code>.</li> <li>The second element of <code>is</code> depends on the second element of <code>ss</code> and on the first element of <code>is</code>.</li> <li>The third element of <code>is</code> depends on the third element of <code>ss</code> and on the second element of <code>is</code>.</li> <li>Etc.</li> </ol> <p>No element of <code>is</code> depends on itself, or on a later element of <code>is</code>.</p></li> </ol>

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