Piglet Part4 - AST
    
    
    
      A language named Piglet to describe the flow chart
    
    
    
      AST
In short
  prog { type: “prog”, consequent: [ …AST ] }
  node { type: “node”, value: string }
  if { type: “if”, test: AST, consequent: [ …AST ], alternate: AST }
  switch { type: “switch”, ...