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diff --git a/software/haskell.page b/software/haskell.page new file mode 100644 index 0000000..8e7d9f8 --- /dev/null +++ b/software/haskell.page @@ -0,0 +1,62 @@ + +Haskell +================== + +Structure +------------ +Haskell programs consist of monads, actions, modules, ??? + +Basic Syntax +--------------- + +A "type declaration": + + main :: IO () + +An action definition. Note that whitespace matters; the block extends to all +lines indented to the same position as the first non-whitespace after the +``do``: + + main = do + stuff1 + stuff2 + +Lists +-------- +Lists in haskell are homogenous: all elements must of the same type. They are +linked lists, so cons-ing on the front is cheap and concatonating on the end +can be expensive. + +Use ++ to concatonate two lists together: + + ['a','b','c'] ++ ['d','e','f'] + +Use : to cons (prepend) a single element: + + 0:[1,2,3,4,5,6] + +Use !! to pull out an element by index (zero indexed): + + ['c','a','t'] !! 1 + +Strings are lists of characters: "baby" is equivalent to ['b','a','b','y'], +which is equivalent to 'b':'a':'b':'y':[]. The empty set is [] and is distinct +from [[]]. + +A couple functions help; 'head' is like 'car' and gives the first element, +'tail' is like 'cdr' and gives everything except the first element, 'last' +gives the last non-empty element, and 'init' gives everything except the +'last'. 'length' gives the number of elements, 'null' is a test to see if this +is the empty list, + +Compilation +------------ +By default the "main" action of the "Main" module is the action that is +executed when a compiled haskell program is run by the operating system; +this means that most haskell programs need to define these components. + +The `ghc` (Glasgow Haskell Compiler) is the most popular. To compile and +execute a simple one file haskell program you will do something like: + + ghc -o hello helloworld.hs + ./hello |