Entries Tagged 'Haskell' ↓

If you like a tool, never look at its headers.

Following hot on the heels of this astonishing header from Boost, here are some excerpts from the module defining tuples in the Glasgow Haskell Compiler:

data (,) a b = (,) a b
    deriving Generic
data (,,) a b c = (,,) a b c
    deriving Generic

(If you can’t read Haskell: (,) a b is another notation for (a, b). This defines types for two- and three-element tuples, with a default implementation of the Generic interface.) Okay so far? The file proceeds to define 4-tuples, 5-tuples, and so on until we get to the 8-tuple definition:

data (,,,,,,,) a b c d e f g h = (,,,,,,,) a b c d e f g h
    -- deriving Generic

Surprise commented-out deriving clause! But it’s all plain sailing from here… until we get to 63-tuples:

data (,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,) a b c d e f g h i j k l m n o p q r s t u v w x y z a_ b_ c_ d_ e_ f_ g_ h_ i_ j_ k_ l_ m_ n_ o_ p_ q_ r_ s_ t_ u_ v_ w_ x_ y_ z_ a__ b__ c__ d__ e__ f__ g__ h__ i__ j__
 = (,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,) a b c d e f g h i j k l m n o p q r s t u v w x y z a_ b_ c_ d_ e_ f_ g_ h_ i_ j_ k_ l_ m_ n_ o_ p_ q_ r_ s_ t_ u_ v_ w_ x_ y_ z_ a__ b__ c__ d__ e__ f__ g__ h__ i__ j__
    -- deriving Generic
{- Manuel says: Including one more declaration gives a segmentation fault.
data (,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,) a b c d e f g h i j k l m n o p q r s t u v w x y z a_ b_ c_ d_ e_ f_ g_ h_ i_ j_ k_ l_ m_ n_ o_ p_ q_ r_ s_ t_ u_ v_ w_ x_ y_ z_ a__ b__ c__ d__ e__ f__ g__ h__ i__ j__ k__
 = (,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,) a b c d e f g h i j k l m n o p q r s t u v w x y z a_ b_ c_ d_ e_ f_ g_ h_ i_ j_ k_ l_ m_ n_ o_ p_ q_ r_ s_ t_ u_ v_ w_ x_ y_ z_ a__ b__ c__ d__ e__ f__ g__ h__ i__ j__ k__

…followed by commented-out definitions of everything up to 100-tuples.

Yesod web application dependencies

I have been experimenting with using Yesod to throw together a web application or two. My experience so far has been broadly positive—if you like computers to check things for you, I recommend it.1 That said, watching the full chain of dependencies fly past was moderately entertaining:2

parsec-3.1.2

An excellent parser-combinator library, widely imitated. This wouldn’t be funny, except…

attoparsec-0.10.1.0

Another excellent parser-combinator library, inspired by parsec.

base-unicode-symbols-0.2.2.3

This defines a bunch of Unicode aliases for standard functions with boring ASCII names. Why write:

x `elem` xs

when you could write:

x ∈ xs

Invaluable!

utf8-light-0.4.0.1 and utf8-string-0.3.7

Two UTF-8 encoding libraries!

semigroups-0.8

“In mathematics, a semigroup is an algebraic structure consisting of a set together with an associative binary operation. A semigroup generalizes a monoid in that there might not exist an identity element. It also (originally) generalized a group (a monoid with all inverses) to a type where every element did not have to have an inverse, thus the name semigroup.”

  1. assuming you like deciphering compiler error messages when the computer says no, that is []
  2. for a quiet Wednesday morning… []