CoffeeScript book examples

02_functions.coffee

refine = (x, y...) ->
  console.log "required: #{x}"
  console.log "optional: #{y.join(', ')}" if y.length > 0

walk = (head, tail...) ->
  console.log head
  walk.apply(@, tail) if tail.length

# Exercises
start = (num) ->
  console.log "\n-----------------------------"
  console.log "Exercise #{num}"
  console.log "-----------------------------\n"
  
# 1.
start 1

console.log "original"
clearArray = (arr) ->
  arr.splice 0, arr.length

console.log clearArray [1,2,3]

console.log "cleared array"
clearArray = (arr) ->
  arr.splice 0, arr.length
  arr

console.log clearArray [1,2,3]

console.log "nothing"
clearArray = ->

console.log clearArray [1,2,3]

# 2.
start 2

run = (fn, args...) -> fn.apply(@, args)
run console.log, 1,2,3

# 3.
start 3

console.log "What does the question mean?"

# 4.
start 4

console.log '''
Whitespace becomes significant in CoffeeScript argument lists because
the interpreter needs to be able to tell the difference between the start
of an argument list and the arguments in it.

For example

f(a,b) passes a,b to f
f a, b also passes a,b to f

But

f (a, b) will attempt to pass (a,b) to f - which causes a syntax error

Interestingly, f (a) works as expected
'''

# 5.
start 5

console.log '''
foo.bar.baz() context = foo.bar
@hoo() context = (current context)
@hoo.rah() context = (current content).hoo
'''

# 6.
start 6

xInContext = ->
  console.log @x

what = {x: 'quantum entanglement'}

xInContext.apply(what)

# 7.
start 7

console.log '''
Yes.

There are 2 vars named x.  In the outer scope x is true and then that is bound to the
locally scoped x inside the function
'''

x = true
showAnswer = (x = x) ->
  console.log if x then 'It works' else 'Nope'
showAnswer()

console.log '''

Wrong!

The argumement list is running in a totally separate context.  Even using @x doesnt work!
'''

@x = true
showAnswer = (x = @x) ->
  console.log if x then 'It works' else 'Nope'
showAnswer()

99_prompt.coffee

# 5x5 example

stdin = process.openStdin()
stdin.setEncoding 'utf8'
GRID_SIZE = 5

inputCallback = null
stdin.on 'data', (input) -> inputCallback input

inRange = (x,y) ->
  0 <= x <= GRID_SIZE and 0 <= y <= GRID_SIZE

isInteger = (num) -> num is Math.round(num)

strToCoordiantes = (input) ->
  halves = input.split(',')
  x = parseFloat(halves[0])
  y = parseFloat(halves[1])
  if halves.length is 2
    if !isInteger(x) or !isInteger(y)
      console.log "Both coordinates must be integers"
    else if not inRange(x,y)
      console.log "Coordinates out of range - 1 to #{GRID_SIZE}"
    else
      {x,y}
  else
    console.log "Inputs must be of the form `x, y`."

promptForTile1 = ->
  console.log "Please enter coordinates for the first tile."
  inputCallback = (input) ->
    promptForTile2() if strToCoordiantes input

promptForTile2 = ->
  console.log "Please enter coordisnates for the second tile."
  inputCallback = (input) ->
    if strToCoordiantes(input) 
      console.log "Swapping tiles...done"
      promptForTile1()


console.log "Welcome to 5x5"
promptForTile1()