The layout rule for indentation must be implemented in the lexer with the new syntax of #69.

• After a do, match, or when, emit a { if one is not present and push the indentation of the next token on to the stack.
• If a line starts at the same indentation as the top of the indentation stack and the previous token was not a ;, then emit a ;.
• If a line starts at a smaller indentation than the top of the indentation stack then pop indentations off the stack until the current indentation is seen, and emit one } for each pop minus the number of } that were seen.
• If a line starts at a greater indentation than the top of the stack then do nothing.