PhraseCache is a simple language for matching user input.

A PhraseCache expression can consist of:

  -just a word or phrase, e.g.:
  
    school
    lunch time

  -a quoted string, e.g.:
  
     "q&a"
     "\o/"
     
   These strings can contain any special character. They are
   matched exactly character-by-character, but are
   case-insensitive. The pattern does not match when it's part
   of a bigger word (e.g. the first example would not match
   the input "faq&answers").
   
   You can even match quotes, like this:
   
     "\"hello\""
     
   This will only match a "hello" put in quotes by the user.
   
  -"or" combination
  
     fun, enjoy
    
   matches "this is fun" as well as "I am enjoying this".
    
  -"and" combination
  
     this + that
    
   matches "this and that" and "that or this", but not
   "this one" or "that one".
   
   "and" takes precedence over "or", so:
   
     the + solution, a + resolution
     
   is the same as:
   
     (the + solution), (a + resolution)
     
   (See "bracketing" below.)
  
  -negation
  
     great + !not
  
   matches "this is great", but not "this is not that great".
    
  -match start of line
  
     ^hello bot
    
   will match "oh hello bot", but not "hello bot friend".
  
  -match end of line
  
     please do this$
     
   will match "now please do this", but not "please do this now".
   
  -bracketing (grouping)
  
     (quick, fast) + (solution, resolution)
    
   will match "we need a fast solution" as well as "the
   resolution should be quick".
   
  -disallow typos with exclamation mark, e.g.:
  
     hi!
     
   By default, PhraseCache has a crude typo detection system
   that allows one typo (1 character added, removed or inserted
   per input row). It's a cool feature, but arguably could see
   some improvement. For naive patterns, it sometimes fails
   badly, e.g. input "I" will also match the pattern "hi".
   
   To circumvent this, add an exclamation mark AFTER the phrase
   in question. (Not before the phrase as that would mean
   negation.)
  

Advanced features (not really used currently):

  -add a weight to a sub-pattern:
  
    (foo, bar)*0.5