Write You a Haskell Stephen Diehl

Design of ProtoHaskell
Now that we’ve completed our simple little ML language, let’s discuss the road ahead toward building a
more complex language we’ll call ProtoHaskell that will eventually become the full Fun language.
Language Chapters Description
Poly 1 - 8 Minimal type inferred ML-like language.
ProtoHaskell 8 - 18 Interpreted minimal Haskell subset.
Fun 18 - 27 ProtoHaskell with native code generator.
e defining feature of ProtoHaskell is that is independent of an evaluation model, so hypothetically
one could write either a lazy or strict backend and use the same frontend.
Before we launch into writing compiler passes let’s look at the overview of where we’re going, the scope
of what we’re going to do, and what needs to be done to get there. We will refer to concepts that are not yet
introduced, so keep is meant to be referred to as a high-level overview of the ProtoHaskell compiler pipeline.
Haskell: A Rich Language
Haskell itself is a beautifully simple language at its core, although the implementation of GHC is arguably
anything but simple! e more one digs into the implementation the more it becomes apparent that a
lot of care and forethought was given to making the frontend language as expressive as it is. Many of
these details require a great detail of engineering work to make them work as seamlessly as they do.
Consider this simple Haskell example but note how much of an extension this is from our simple little
ML interpreter.
filter :: (a -> Bool) -> [a] -> [a]
filter pred [] = []
filter pred (x:xs)
| pred x = x : filter pred xs
| otherwise = filter pred xs
Consider all the things that are going on just in this simple example.
• Lazy evaluation
• Custom datatypes
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