Editing Inlining and Specialisation (section)

= What does the <code>INLINE</code> pragma do? =

The <code>INLINE</code> pragma can be applied to top-level definitions. It behaves like the <code>INLINABLE</code> pragma but makes GHC very keen to inline the function.

<pre class="haskell">mySimpleFunction :: ...
mySimpleFunction = ...

{-# INLINE mySimpleFunction #-}</pre>
It is a sledgehammer and without care you can make the compiler take a long time and produce a lot of code. Most &quot;ticks exhausted&quot; panics are due to library authors misusing <code>INLINE</code> pragmas.

Liberally sprinkling all your definitions with <code>INLINE</code> is likely make the compiler take a very long time to compile your program. It is not beneficial to inline every function, inlining a function which is not optimised further only increases overall code size without improving performance.

One situation where it is useful to use an <code>INLINE</code> pragma is when the definition of the function contains functions which are mentioned in <code>RULES</code>. In this case, it is essential that the optimiser is quite aggressive so that the <code>RULES</code> can fire.