% Write You a Haskell
% Stephen Diehl
% 1/2/2015

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Forward
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In 2014 I wrote a [short tutorial](http://www.stephendiehl.com/llvm/) about
building a small imperative language in Haskell that compiled into LLVM. I was
extremely happy with the effect the tutorial seemed to have, and the warm
response I got from so many people was very encouraging.

I've done a great bit of thinking about what the most impactful topic I could
write about in 2015 could be; and decided throughout this year I will follow up
with an large endeavor for another project-based tutorial on *building a simple
functional programming language from first principles*.

This is a nontrivial topic and is unfortunately very much underserved, the
knowledge to build such a modern functional language is not widely disseminated
among many programmers.  The available resources most often discuss language
theory in depth while completely glossing over the engineering details. I wished
to write a project-based tutorial that included the engineering details and left
the reader with a fully functional toy language at the end that could be
extended for further projects.

We will build a small functional language called *Fun* which is a partial
Haskell 2010 toy language; complete with a parser, type inference, datatypes,
pattern matching, desugaring, typeclasses, higher-kinded types, monadic IO,
arbitrary-rank polymorphism, records, Core language, STG intermediate language,
lazy evaluation, interpreter, native code generator, a runtime, and several
optimization passes.

As with most of my writing, this is the pre-edited rough cut version, which I
will refine over time. The compiler itself is fully complete as of December
2014, but each of the chapters (28 in total) will be staggered on a
month-by-month basis to allow me to progressively refine the text with feedback
from readers and testers.  The later chapters on runtime and code generation are
somewhat involved and much longer.

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\textit{Stephen Diehl}
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