Well, I'm about 5 weeks into Introduction to Functional Programming, a.k.a. FP101x, an online class taught in Haskell by Eric Meijer. The class itself is a couple weeks ahead of that; I'm lagging a bit. So, how is it so far, you ask?
The first 4 weeks covered basic functional concepts and how to express them in Haskell, closely following chapters 17 of the book, Graham Hutton's Programming in Haskell:
 Defining and applying functions
 Haskell's type system
 parametric types
 type classes
 type signatures of curried functions
 pattern matching
 list comprehensions
 recursion
 higherorder functions
Haskell's hierarchy of type classes is elegant, but some obvious things seem to be missing. For example, you can't show
a function. But, it would be really helpful to show something like a docstring, or at least the function's type signature. Also machineword sized Int
's don't automatically promote, so if n
is an Int
, n/5
produces a type error.
Most of the concepts were familiar already from other functional languages, Scheme via SICP, OCAML via Dan Grossman's programming languages class, and Clojure via The Joy of Clojure. So, this early part was mostly a matter of learning Haskell's syntax.
Some nifty examples
a recursive definition of factorial:
factorial :: Integer > Integer factorial 0 = 1 factorial n = n * (factorial (n1))
sum of the first 8 powers of 2:
sum (map (2^) [0..7])
a recursive definition of map:
map :: (a > b) > [a] > [b] map f [] = [] map f (x:xs) = f x : map f xs
get all adjacent pairs of elements from a list:
pairs :: [a] > [(a,a)] pairs xs = zip xs (tail xs)
check if a list of elements that can be ordered is sorted by confirming that each pair of elements is ordered:
sorted :: Ord a => [a] > Bool sorted xs = and [x <= y (x,y) < pairs xs]
Haskell attains its sparse beauty by leaving a lot implied. One thing I figured out during my brief time with OCAML also seems to apply to Haskell. Although these languages lack the forest of parentheses you'll encounter in Lispy languages, it's not that the parentheses aren't there; you just can't see them. A key to reading Haskell is understanding the rules of precedence, associativity and fixity that imply the missing parentheses.
Pre cedence  Left associative  Non associative  Right associative 

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Another key is reading type signatures of curried functions, as that is the default in Haskell and is relied upon extensively in composing functions, particularly in the extra terse "pointfree" style.
Currently, I'm trying to choke down Graham Hutton's Addendum on Monads. If I end up understanding that, it'll get me a codemonkey merit badge, for sure.