A pretty printer:

• parses input source
• prints it, perhaps with improved formatting
  • e.g. HTML listing, documentation, latex

Simple pretty printer is in tree.scala

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

Use of pretty printer to test a parser

Possible improvements to simple pretty printer

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