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    <p>As far as I can tell, <code>primitiveBindings</code> is <em>not</em> a global environment, but rather an action that, when performed, generates a fresh mapping with the primitive bindings already set up. Perhaps a better name for it would have been <code>createPrimitiveBindings</code>. There is no way to have proper globals in Haskell without <code>unsafePerformIO</code> hacks. </p> <p>Therefore, the way you're trying to add <code>eval</code> would make it evaluate everything in a <em>new</em> environment, since you're re-running the <code>primitiveBindings</code> action. We can easily take care of the type errors, if that is indeed what you intended:</p> <pre><code>baseFun :: [(String, [LispVal] -&gt; IOThrowsError LispVal)] baseFun = [("eval", evalInNewEnv)] where evalInNewEnv args = do env &lt;- liftIO primitiveBindings unaryOp (eval env) args </code></pre> <p>As you see, there is no need for any <code>readIORef</code> here, since <code>eval</code> already expects <code>Env</code> which just a type synonym for an <code>IORef</code>.</p> <p>However, it sounds to me like you'd like <code>eval</code> to work in a "global" environment, in which case, you would need to have this environment passed to you somehow, since as I mentioned, there are no globals. For example, we can define something like this which would create a new environment with <code>eval</code> in it. </p> <pre><code>primitiveBindingsWithEval :: IO Env primitiveBindingsWithEval = do env &lt;- primitiveBindings bindVars env [("eval", unaryOp (eval env))] </code></pre> <p>You can then replace existing uses of <code>primitiveBindings</code> with <code>primitiveBindingsWithEval</code> when you want a fresh environment with <code>eval</code> in it.</p>
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    1. POGetting element out of IO in Haskell
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    1. COYour fixing of the type errors isn't quite right, since the return type of `unaryOp` doesn't support `IO`. You'll need to generalise the type of `unaryOp` before you can use it like that.
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    2. COThis answer and benmachine followup is what makes a click in my brain! As nice bonus this fixes problem I did not know I had had. I truly appreciate the help. Thank you.
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