org-mode-utf8-exported.txt

                            ━━━━━━━━━━━━━━━━
                             HASKELL-NOTES1


                             Fernando Basso
                            ━━━━━━━━━━━━━━━━


Table of Contents
─────────────────

1 Intro
.. 1.1 More stuff
..... 1.1.1 Even more text
2 Some code examples
.. 2.1 Example One: Doubles
.. 2.2 Example Two: Rectangle Area


1 Intro
═══════

  Haskell is purely functional.

  No changing state.

  “In purely functional programming you don't tell the computer what to
  do as such but rather you tell it what stuff is. The factorial of a
  number is the product of all the numbers from 1 to that number, the
  sum of a list of numbers is the first number plus the sum of all the
  other numbers, and so on. You express that in the form of functions.”


1.1 More stuff
──────────────

  No side effects. Functions calculate something and return that value.

  Referential Transparency: if you call the same function multiple times
  with the same arguments, it is guaranteed to always return the same
  result.

  Evaluates things /lazily/ (only when needed).

  Think of programs as a series of *transformations on data*.

  *Statically Typed*: (types are checked at compile time instead of at
   runtime).


1.1.1 Even more text
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

  *Type Inference*


  `.hs' extension, generally.

  Load and reload code from a file in ghci:

  `ghci' to start the interactive prompt, then `:load functions.hs' from
  the same directory. Tab completion worksr; extension is not required.

  `:reload' reloads the loaded file.

  `:load' can be just `:l', and `:reload' can be just `:r'.

  ┌────
  │ 2 * (-2) -- Omitting the parenthesis is an error.
  └────


  `==' means ‘equal to’.  `/=' means ‘not equal to’, or ‘different
  than’. (like `!=' in other languages).  `not' negates (like `!' in
  other languages).

  `+' works for things that can be considered numbers (~'5'~ and ~"5"~
  do cannot).  `==' works for things that can be compared (`5 == 5' or
  ~"foo" `= "bar"~ can be comapared, but 5 =' "5" cannot).

  5 can act like 5.0, but 5.0 cannot act like 5 (it would lose
  precision).


  `*' is a function and it is used with _infix_ notation, contrary to
  functions that are used with _prefix_ notation.

  `5 `div` 2.5' is an error. `5 / 2.5' is not

  Function Application (invoke/call a function) has the highest
  precedence.

  Syntax test:

  Copy `~/.emacs.d/foo.el' to wherever yo want.


2 Some code examples
════════════════════

  May the source be with you.


2.1 Example One: Doubles
────────────────────────

  doubles:
  ┌────
  │ double num = num * 2
  │ quadruple someNum = double (double someNum)
  │ square i = i * 2
  │ half x = x / 2
  └────


2.2 Example Two: Rectangle Area
───────────────────────────────

  Example: Rectangle Area:
  ┌────
  │ areaRect l w = l * w
  │ areaTriang b h = (b * h) / 2
  └────