###
  Add a pattern i.e. a substitution rule.
  Substitution rule needs a template as first argument
  and what to transform it to as second argument.
  Optional third argument is a boolean test which
  adds conditions to when the rule is applied.
###

# same as Eval_pattern but only leaves
# NIL on stack at return, hence gives no
# printout
Eval_silentpattern = ->
  Eval_pattern()
  pop()
  push_symbol(NIL)

Eval_pattern = ->
  # check that the parameters are allright
  if !iscons(cdr(p1))
    stop("pattern needs at least a template and a transformed version")
  firstArgument = car(cdr(p1))
  secondArgument = car(cdr(cdr(p1)))
  if secondArgument == symbol(NIL)
    stop("pattern needs at least a template and a transformed version")
  # third argument is optional and contains the tests
  if !iscons(cdr(cdr(p1)))
    thirdArgument = symbol(NIL)
  else
    thirdArgument = car(cdr(cdr(cdr(p1))))

  if equal(firstArgument, secondArgument)
    stop("recursive pattern")

  # console.log "Eval_pattern of " + cdr(p1)
  # this is likely to create garbage collection
  # problems in the C version as it's an
  # untracked reference
  stringKey = "template: " + print_list(firstArgument)
  stringKey += " tests: " + print_list(thirdArgument)
  if DEBUG then console.log "pattern stringkey: " + stringKey

  patternPosition = userSimplificationsInStringForm.indexOf stringKey
  # if pattern is not there yet, add it, otherwise replace it
  if patternPosition == -1
    #console.log "adding pattern because it doesn't exist: " + cdr(p1)
    userSimplificationsInStringForm.push(stringKey)
    userSimplificationsInListForm.push(cdr(p1))
  else
    if DEBUG then console.log "pattern already exists, replacing. " + cdr(p1)
    userSimplificationsInStringForm[patternPosition] = stringKey
    userSimplificationsInListForm[patternPosition] = cdr(p1)

  # return the pattern node itself so we can
  # give some printout feedback
  push_symbol(PATTERN)
  push cdr(p1)
  list(2)
  

###
  Clear all patterns
###


do_clearPatterns = ->
  userSimplificationsInListForm = []
  userSimplificationsInStringForm = []

Eval_clearpatterns = ->
  # this is likely to create garbage collection
  # problems in the C version as it's an
  # untracked reference
  do_clearPatterns()
  
  # return nothing
  push_symbol(NIL)


Eval_patternsinfo = ->
  patternsinfoToBePrinted = patternsinfo()

  if patternsinfoToBePrinted != ""
    push new_string(patternsinfoToBePrinted)
  else
    push_symbol(NIL)

patternsinfo = ->
  patternsinfoToBePrinted = ""
  for i in userSimplificationsInListForm
    patternsinfoToBePrinted +=  userSimplificationsInListForm + "\n"
  return patternsinfoToBePrinted