Catch missing parens

[benbc]

Not sure that I'm holding the error hierarchy right. I tried to use the fancy DeferLineInfo stuff, but I couldn't make that work at this point in the parser.

So the error that this produces isn't particularly user-friendly.

This line (missing a terminal paren):

Ideas > Options @ Rate(IdentificationR * (PMs - (PMDeliveryBurden * Deliverables))

Gives this error:

$ cat error.sys | systems-run
Traceback (most recent call last):
  File "/home/benbc/.pyenv/versions/3.10.5/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/home/benbc/.pyenv/versions/3.10.5/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/home/benbc/src/lethain/systems/systems/parse.py", line 143, in <module>
    main()
  File "/home/benbc/src/lethain/systems/systems/parse.py", line 129, in main
    model = parse(txt)
  File "/home/benbc/src/lethain/systems/systems/parse.py", line 86, in parse
    _, tokens = lexer.lex(txt)
  File "/home/benbc/src/lethain/systems/systems/lexer.py", line 179, in lex
    line.append(lex_flow(char_buff))
  File "/home/benbc/src/lethain/systems/systems/lexer.py", line 134, in lex_flow
    return lex_caller(TOKEN_FLOW, txt)
  File "/home/benbc/src/lethain/systems/systems/lexer.py", line 113, in lex_caller
    params = lex_parameters(rest)
  File "/home/benbc/src/lethain/systems/systems/lexer.py", line 97, in lex_parameters
    return (TOKEN_PARAMS, tuple([lex_formula(x) for x in params]))
  File "/home/benbc/src/lethain/systems/systems/lexer.py", line 97, in <listcomp>
    return (TOKEN_PARAMS, tuple([lex_formula(x) for x in params]))
  File "/home/benbc/src/lethain/systems/systems/lexer.py", line 76, in lex_formula
    raise systems.errors.MismatchedParens(txt)
systems.errors.MismatchedParens: MismatchedParens for formula 'IdentificationR*(PMs-(PMDeliveryBurden*Deliverables)'