trs/TODO

# vim: set fileencoding=utf-8 :

 - Fix BisonSyntaxError location tracking.

 - Sort polynom by its exponents?

 - Fix division by zero caused by "0/0": Catch exception in front-end

smvv@multivac ~/work/trs $ printf "a/0\n??" | ./main.py
Traceback (most recent call last):
  File "./main.py", line 75, in <module>
    main()
  File "./main.py", line 64, in main
    node = p.run(debug=args.debug)
  File "/home/smvv/work/trs/external/pybison/src/python/bison.py", line 258, in run
    self.report_last_error(filename, e)
  File "/home/smvv/work/trs/external/pybison/src/python/bison.py", line 251, in run
    self.engine.runEngine(debug)
  File "bison_.pyx", line 592, in bison_.ParserEngine.runEngine (build/external/pybison/bison_.c:592)
  File "/home/smvv/work/trs/src/parser.py", line 195, in hook_handler
    possibilities = handler(retval)
  File "/home/smvv/work/trs/src/rules/fractions.py", line 23, in match_constant_division
    raise ZeroDivisionError('Division by zero: %s.' % node)
ZeroDivisionError: Division by zero: a / 0.

smvv@multivac ~/work/trs $ printf "0/0\n??" | ./main.py
Traceback (most recent call last):
  File "./main.py", line 75, in <module>
    main()
  File "./main.py", line 64, in main
    node = p.run(debug=args.debug)
  File "/home/smvv/work/trs/external/pybison/src/python/bison.py", line 258, in run
    self.report_last_error(filename, e)
  File "/home/smvv/work/trs/external/pybison/src/python/bison.py", line 251, in run
    self.engine.runEngine(debug)
  File "bison_.pyx", line 592, in bison_.ParserEngine.runEngine (build/external/pybison/bison_.c:592)
  File "/home/smvv/work/trs/src/parser.py", line 195, in hook_handler
    possibilities = handler(retval)
  File "/home/smvv/work/trs/src/rules/numerics.py", line 73, in match_divide_numerics
    divide = not divmod(n.value, dv)[1]
ZeroDivisionError: integer division or modulo by zero

 - Last possibilities reduce to a similar result.

smvv@multivac ~/work/trs $ printf "0/1\n??" | ./main.py
<Possibility root="0 / 1" handler=divide_numerics args=(0, 1)>
Division of 0 by 1 reduces to 0.
Division of 0 by 1 reduces to 0.

 - Fractions constant rewrite rules.

 - >>> (sin x) ^ 2 + (cos x) ^ 2
   sin(x) ^ 2 + cos(x) ^ 2
   >>> sin(x) ^ 2 + cos(x) ^ 2
   sin(x ^ 2) + cos(x ^ 2)

 - ExpressionNode.equals() werkend maken voor alle cases (negatie).

 - validation: preorder traversal implementatie vergelijken met andere
               implementaties.

 - Fix the following loop using strategy (reduce_fraction_constants):
   >>> 2 / 7 - 4 / 11
   2 / 7 - 4 / 11
   >>> @
   22 / 77 - 28 / 77
   >>> @
   2 / 7 - 28 / 77
   >>> @
   2 / 7 + 4 / 11

 - Cancel terms before multiplying constants: (3 * ...) / (3 * ...) -> ... / ...
    >>> (7/3)*(3/5)
    7 / 3 * (3 / 5)
    >>> ??
    Expand fraction with nominator greater than denominator 7 / 3 to an integer
    plus a fraction.
    Multiply fractions 7 / 3 and 3 / 5.
    >>> @
    7 * 3 / (3 * 5)
    >>> ?
    Multiply constant 7 with 3.
    >>> @
    21 / (3 * 5)
    >>> @
    21 / 15
    >>> @
    7 / 5

 - Fix error while parsing unicode PI:
   >>> sin(1/2 * pi)
   sin(1 / 2 * π)
   >>> @
   unknown char � ignored.
   unknown char � ignored.
   ERROR: 41.7-41.8: "syntax error, unexpected TIMES" near "*".
   ERROR: 41.14-41.15: "syntax error, unexpected RPAREN" near ")".

 - No matches for sin(pi), sin(2pi), sin(4pi), etc...

 - Create unit tests for node inequivalence operator.

 - Line printer: 1 / (n + n)x  ->  1 / (n + n) * x

 - Parser: 'apia' -> 'aa'

 - 'x(1 / x)'  ->  '(x * 1) / x'  (currently no left/right check: '1x / x')

 - Unit tests for strategy.

 - MESSAGES needs to be expanded.

 - Use pretty-print for expressions in hint messages.

 - Parser:
   + add unit tests for operator associativity (derivatives/integrals).
   + plus << integral/derivative << times
   + divide >> times
   + a2 -> a*2 instead of a^2