Invisible <voi### [at] devnull> wrote:
> Anything that isn't parsable as a number is a name. Therefore,

> "0."    -> real
> ".0"    -> real
> "."     -> name
> "1.1"   -> real
> "1.1.1" -> name
> "1e1"   -> real
> "1x1"   -> name
> "s1"    -> name
> "1s"    -> name

> Will the insanity never end?? >_<

> Good luck writing a parser that can untangle all of that... :-(

  I really can't see the problem. When the input contains a sequence of
valid characters (ie. which can form a real or a name), if this sequence
has the form:

    ^[+-]?([0-9]+\.?|[0-9]*\.[0-9]+)(e[+-]?([0-9]+\.?|[0-9]*\.[0-9]+))?$

then it's a real, else it's a name.

  If we translate that regexp to plain English, it means:

- There's nothing before this pattern (which is what the ^ at the beginning
  means), and nothing after it (which is what the $ at the end means).
- The sequence optionally starts with a + or a -.
- After that two possible patterns must appear (the expression in
  parentheses, where the two patterns are separated with the | symbol):
  - A sequence of one of more digits ([0-9]+), optionally followed by
    the dot character (a plain "." has a special meaning in regexps, so the
    dot character has to be escaped, and thus written as "\.")
  - A sequence of zero or more digits ([0-9]*) followed by a dot character
    followed by a sequence of one of more digits.
- Optionally the character "e" can follow, and if that's the case, a real
  (not containing an "e") must follow as well (the whole last part in
  parentheses, with the "?" at the end to indicate optionality).

  In an actual BNF-style parser the rule probably becomes simpler because
the repetition can be removed.

-- 
                                                          - Warp

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