Convert a Forsyth-Edwards Notation string to ASCII art
Retina, 13 bytes

\d
$* 
/
¶

|


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Explanation

The first part (note the trailing space):

\d
$* 


is to convert a to the specific number of spaces. Retina has a $* feature to repeat. The way it works is: &lt;num&gt;$*&lt;char&gt; if there is no &lt;num&gt;, Retina will assume $&amp; or the matched string, in this case the matched number.

The next part:

/
¶


is pretty simple, it replaces all / with ¶ which is a newline.

The last part works the same:

    
|

This will replace everything (hence why there is nothing on the first line) with |. Putting a | everywhere.