Goal

Provide adequate, but non intrusive feedback to user about syntax errors.

Parser

1. Should only parse when neccessary:
   1. When editing a new or correct expression:
      1. After typing a point, comma, colon, semi-colon, space, tab or line-break; or leaving the edited word
      2. After leaving the edited expression (using cursor or mouse)
   2. When editing a incorrect expression:
      1. After each added character
2. Provide errors in adequate datastructure to visualisation components
   1. linenumber
   2. type of error
   3. further information
3. Whenever the visualisation of an expression should change, the parser should call an event handler provided by visualization components

  Note:
  * A new expression is correct until it becomes incorrect.
  * The state of an expression can only be changed when the cursor leaves it.

Visualization

1. Provides event handler and registers it to parser error-event
2. Underline syntax errors using a (preferably wavy) red line
3. On mouse over, show information on error
4. Information window could be clickable to provide further error information

Suggestions

1. To be implemented after parser and visualization components are feature complete
2. Suggestions based on information from parse tree
3. Analyzation based on soundex or other algorithm