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<p style="margin: 1.2em 0px ! important;">If your
instance-generating function is defined in an external module,
you can use it in GHCi like this:</p>
<pre style="font-size: 0.85em; font-family: Consolas,Inconsolata,Courier,monospace;font-size: 1em; line-height: 1.2em;margin: 1.2em 0px;"><code style="font-size: 0.85em; font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px; display: inline;white-space: pre; overflow: auto; border-radius: 3px; border: 1px solid rgb(204, 204, 204); padding: 0.5em 0.7em; display: block ! important;display: block; padding: 0.5em; color: rgb(51, 51, 51); background: rgb(248, 248, 255) none repeat scroll 0% 0%;" class="hljs language-haskell"><span class="hljs-comment">-- Enable TH</span>
> :set -<span class="hljs-type">XTemplateHaskell</span>
<span class="hljs-comment">-- Import modules (e.g. Aeson)</span>
> <span class="hljs-import"><span class="hljs-keyword">import</span> Data.Aeson.TH</span>
> <span class="hljs-import"><span class="hljs-keyword">import</span> Data.Aeson</span>
<span class="hljs-comment">-- Define the type for which I'm going to generate instances</span>
> <span class="hljs-typedef"><span class="hljs-keyword">data</span> <span class="hljs-type">X</span> = <span class="hljs-type">X</span> <span class="hljs-container">{<span class="hljs-title">x</span> :: <span class="hljs-type">Int</span>}</span></span>
<span class="hljs-comment">-- Derive the instance</span>
<span class="hljs-type">Prelude</span> <span class="hljs-type">Data</span>.<span class="hljs-type">Aeson</span>.<span class="hljs-type">TH</span>> <span class="hljs-typedef"><span class="hljs-keyword">data</span> <span class="hljs-type">Dummy</span>; deriveJSON defaultOptions ''<span class="hljs-type">X</span></span>
<span class="hljs-comment">-- Check that it works</span>
> toJSON (<span class="hljs-type">X</span> <span class="hljs-number">1</span>)
<span class="hljs-type">Object</span> (fromList [(<span class="hljs-string">"x"</span>,<span class="hljs-type">Number</span> <span class="hljs-number">1.0</span>)])
</code></pre>
<p style="margin: 1.2em 0px ! important;">(More about the <code style="font-size: 0.85em; font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px; display: inline;">data Dummy</code>
trick here: <a
href="https://www.reddit.com/r/haskelltil/comments/3ghacj/you_can_use_template_haskell_functions_like/"><a class="moz-txt-link-freetext" href="https://www.reddit.com/r/haskelltil/comments/3ghacj/you_can_use_template_haskell_functions_like/">https://www.reddit.com/r/haskelltil/comments/3ghacj/you_can_use_template_haskell_functions_like/</a></a>.)</p>
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