Problem Statement

Imperative programs like to jump around, but some languages restrict these jumps. Many structured languages restrict their conditional structures and loops to local jumps within a function. Some assembly languages limit certain jumps or branches to a small range. This task is to demonstrate a local jump and a global jump and the various other types of jumps that the language supports. For the purpose of this task, the jumps need not be used for a single purpose and you have the freedom to use these jumps for different purposes. You may also defer to more specific tasks, like Exceptions or Generator. This task provides a "grab bag" for several types of jumps. There are non-local jumps across function calls, or long jumps to anywhere within a program. Anywhere means not only to the tops of functions! These jumps are not all alike. A simple goto never touches the call stack. A continuation saves the call stack, so you can continue a function call after it ends.

Use your language to demonstrate the various types of jumps that it supports. Because the possibilities vary by language, this task is not specific. You have the freedom to use these jumps for different purposes. You may also defer to more specific tasks, like Exceptions or Generator.

Let's start with the solution:

' FB 1.05.0 Win64

' compiled with -lang fb (the default) and -e switches

Sub MySub()
  Goto localLabel
  Dim a As Integer = 10  '' compiler warning that this variable definition is being skipped
  localLabel:
  Print "localLabel reached"
  Print "a = "; a  '' prints garbage as 'a' is uninitialized
End Sub

Sub MySub2()
  On Error Goto handler
  Open "zzz.zz" For Input As #1 '' this file doesn't exist!
  On Error Goto 0 '' turns off error handling
  End

  handler:
  Dim e As Integer = Err '' cache error number before printing message
  Print "Error number"; e; " occurred - file not found"
End Sub

Sub MySub3()
  Dim b As Integer = 2
  On b Goto label1, label2 '' jumps to label2

  label1:
  Print "Label1 reached"
  Return '' premature return from Sub

  label2:
  Print "Label2 reached"
End Sub

Sub MySub4()
  Dim c As Integer = 3
  If c = 3 Goto localLabel2 '' better to use If ... Then Goto ... in new code
  Print "This won't be seen"
  localLabel2:
  Print "localLabel2 reached"
End Sub

MySub
MySub2
MySub3
MySub4
Print
Print "Pres any key to quit"
Print