Haskell Book: Chapters 3 & 4

Chapter 3

• type Char (in single quotes) vs type String (which is as usual syntactic sugar for a list of chars, hence String is a type alias for [Char])

• need main when building a project with Stack

• the IO () type, “used when the result of running a program involves effects beyond evaluating a function or expression”

• print vs putStr vs putStrLn - the first just prints whatever to the display hence, the others are String specific (putStrLn will add a newline char):

  1 2	print "hello" -- "hello" with quotation marks

• do syntax -> used when sequencing actions. Not strictly necessary, used for readability.

• concatenate strings with ++ and concat

• top-level vs. local bindings

• first mention of type classes:

  Type classes provide definitions of operations, or functions, that can be shared across sets of types

• List functions

  • cons or :
  • head
  • tail
  • take
  • drop
  • !! (index)
  • These functions are unsafe:

    while all of these are standard Prelude functions, many of them are considered unsafe. They are unsafe, because they do not know how to handle an empty list. Instead, they throw out an error message, or exception, when given an empty list as input

Chapter 4

• Data declarations

  • type constructor
  • data constructor

• Sum (union) types:

  1	data Bool = False | True