Your example does demonstrate how CS works. When you assign bar a new value inside its original scope, the value of bar does indeed change.

  bar = ->
    "I called bar!"

  foo = ->
    console.log bar()
    bar = "I manually assigned bar!"
    return bar

  console.log foo()
  console.log bar()
  

Here is a slightly less contrived example:

  log = (data) ->
    console.log data
    
  enhance_logging = ->
    i = 0
    log = (data) ->
      i += 1
      console.log i, data

  log "no line numbers"
  enhance_logging()
  log "line one"
  log "line two"
  

Here is the output:

  > coffee foo.coffee 
  no line numbers
  1 'line one'
  2 'line two'