Haskell and the elegant attack.

Welcome back to the Happy Haskell HAckers Tour. As we approach our next stop, let me firstly apologise for the recent detours. Our bus driver, Yoneda, mixed up the maps and started following the GHC After Dark¹ script. But now we’re back on track, and coming up on your left is our monument to the Haskell literals:

-- | motto
--
-- We may need to think more about this (SPJ)
--
motto :: String
motto = "avoid success at all costs"

For a long time, through the darkness of pointfree, the incompatibility of lhs, and the golden age of DerivingVia, this motto has guided Haskell language design. If you peer closely, you’ll notice some scratchings of the original work. These are various attempts at interpretation involving commas and parenthesis, by our bright but cheeky novitiates, but we’ve done our best to restore the work to its original intent.

Archivist retrieval digs have recently confirmed the original context of these words, and now believe it is not a motto at all, but part of a larger computation², one that has been recovered³ from a lost functional pearl⁴

-- | The literals
--
-- Ok, ship it (SPJ)
--
literals :: [String]
literals =
  mconcat $
    fmap List.unwords <$>
    (combinations <$>
     [1 .. 5] <*>
     pure
     (List.words
      "avoid success at all costs"
     ))

Whilst we do not have time to cover all of the technical details⁵, what has previously been described as the Haskell motto, is, in fact, simply a seed string that generates a lexicographically ordered list of aphorisms (the literals).

Note how the seed value is embedded directly in the computation and cannot be changed. One can imagine inserting another motto into the computation, but this would, literally, not be Haskell.

Note also that any combination disrespecting the lexicographic ordering of the seed literal is considered heresy, and will regardless be unavailable to the compiler. Problematic examples that have caused confusion in the past include “success avoid” and “costs avoid success.”

But enough with the theory, if a volunteer would like to step up and spin the literal combinator, that big button marked random-1.2.0, let’s meet the Haskell literals.

-- >>> literal 5
-- avoid success

Or, as Rudyard Kipling (an early adopter of category theory) wrote on the steps of Wimbledon, “meet with triumph and disaster, and treat those two impostors just the same (or at least, up to isomorphism).”

Quoting from the lost pearl, “maybe we should avoid labels such as success being placed on language design. Either they will turn out to be correct, in which case the label is redundant, or they will eventually need replacement, in which case the label becomes an impediment to adopting better ways.”

-- >>> literal 1
-- success

My favourite literal, and one of the singletons. The singletons are best understood as interjections⁶, so an accurate translation is actually Success!.

In the lost pearl, it reads literally as “joy of haskell.” Some other interpretations include “I can’t believe it compiles!”, “Huzzah!”, “Poggers! Let’s goooo!” and, the dryer, “With Haskell, if you can get it to compile, it usually runs.”

-- >>> literal 0
-- avoid

Or Avoid!, the head of the literals. To quote the ancients⁷, “In a functional language with lazy evaluation, we can go a step further and eliminate the recursive definitions … in favour of a more modular solution.” A more modern version is “a bug can only exist if it’s representable.” When laziness is inherent and exposed in language design, we can all get to the point quicker and have some down time.

Avoid!

The Elegant Attack Proclamation

-- >>> literal 30
-- avoid success at all costs

Now Yoneda and I could sit here all day, watching the combinator spin⁸ its way through Hask -> Hask, but that’s our day job, and some of you may be getting bored, so let’s skip to the last of the literals.

In a recent enunciation⁹, literal 30 was described in these terms:

Haskell embodies a radical and elegant attack on the entire enterprise of writing software.

The elegance comes from how the literals combine to form this emerging narrative. For example, this is not the elegant attack but embodies it:

Haskell is a non-commercial (avoid all costs¹⁰), volunteer army (success at all costs¹¹) who would like coders (forall coders.¹²) everywhere (avoid success at¹³) to have rich (success at all¹⁴) lives, with less tedium (Avoid!) and the best (Success!) tools.

Please, a round of applause, and spare change if you have it, for our real-life combinatorial choreographers of language design, who juggle and balance the literals day in and day out, in their quest for software perfection.

And until next time, when we visit the GHC foundry, where tar balls are rendered and frozen, and libraries machined to isomorphic perfection, Yoneda and I will leave you be. Feel free to spin the literal combinator some more, and ponder the Haskell literals and the elegant attack they may formulate.

Finally, literal 7 (avoid all)¹⁵