Consider a pretty printer that:

• parses input source code
• builds abstract syntax tree
• prints abstract syntax tree, perhaps with improved formatting
  • generate again source code
  • create javadoc
  • create input for latex that produces nice listing

Simple pretty printer is in the apply method of Tree.scala

• in Scala, f(x) is a shorthand for f.apply(x)

Operations:

lex   : List[Char] -> List[Token] 
parse : List[Token] -> Tree
print : Tree -> List[Char]

What should we expect to hold:

print(parse(lex(charList)) == charList
parse(lex(print(tree))) == tree

We can use this to test a parser and pretty printer

Possible improvements to simple pretty printer

• emit fewer parantheses
• retain comments and some formatting
• perform semantic checks - a diagnostic tool