[Proj] proj.4 BNF

[Gerald I. Evenden]

On Monday 20 October 2008 11:05:41 pm support.mn at elisanet.fi wrote:
> The problem using + alone as a staement separator is obvious,
> since it can be mixed with positive number sign. One way is to forbid
> to use "+" as a positive number sgn. But then it would trop all
> future expressions also. Maybe best is to agree, that if "+" is
> used as statement separator (and continuation mark) it should
> be preceded by <SEP>, which is usually the case.
>
> So it would be more like:
>
>
> <SEP> ::= (<SPACE>  | <TAB> | <EOL>) {<SEP>}
>
> <continuation> ::= <SEP> "+"
>
>
> That would require some white space before + and would make it
> most clear?
>
> ----
>
> Janne.

I should stay out of this thread other than to discourage it because it is making a grand mountain out of a 
mole hill.

Regarding the "+": it has nothing to do as a separator and if bothering to use BNF, use something like:

<proj_key>::= "+"<id> | <id>

where id is your typical identifier definition.  Treating "+" as a delimiter only confuses the issue.  In fact, treating 
it like white space could cause a failure---"+proj=poly+ellps=intl" would fail becaue the second + would be 
treated as part of the projection name and there is no projection called "+ellps=intl",

<proJ_option> ::= <proj_key> | <proj_key>"="<proj_value>

<proj_option_list> ::=  <proj_option> | <proj_option_list><white_space><proj_option>

<white_space> ::= <white_space_char> | <white_space><white_space_char>

<white_space_char> ::= " " | <tab> | <new_line>

I do not think the above (given it's possible BNF warts and incompleteness> is really necessary as it is a 
common scenario for keyword control entry.  Users may get confused as to what and how of the <proj_key>s 
but I do not think entering the values is that confusing because it is virtually identical to entering runline 
control options.

Alas.

As a final note: it we really want to get serious about BNF and such descriptions of control entry then we may 
have to install a lexical analyzer designed with programs lex or flex and possibly a parsing machine designed 
with yacc or bison.  Do programmers, installers of libproj4 want to get involved with these beasts?

> -----------------------------------------
>
> support.mn at elisanet.fi kirjoitti:
> > Frank Warmerdam <warmerdam at pobox.com> kirjoitti:
> > > support.mn at elisanet.fi wrote:
> > > > Maybe should define the correct BNF (BackusNaur Form) for proj.4?
> > > >
> > > > http://en.wikipedia.org/wiki/Backus-Naur_form
> > > >
> > > > That would help people to write correct proj.4 inits. I am still
> > > > wondering that if sombody enters wrong proj.4 attributes, the library
> > > > takes them in, but does
> > > > something else and never informs the user that something he was
> > > > entering was totally ignored. Not a very nice situation.
> > > >
> > > > There might be some kind of a stand alone pre scanner, that could be
> > > > called on demand and that checked the user entry and gave full
> > > > information about typos. errors and similar matters. It could be
> > > > bypassed by those who do not need it. But I don't see why anybody
> > > > wanted to bypass checking of his input.
> > >
> > > Janne,
> > >
> > > While this seems like a reasonable idea, I am doubtful that it will
> > > occur due to the challenges in implementing and keeping it up to date.
> >
> > Well, I can start with it. Here is an example, maybe full of errors, but
> > something to start with.
> >
> > ------------------
> >
> > <proj.4 definition> ::= <statement list>
> >
> > <statement list> ::= <statement> {<SEP> <statement list> }
> >
> > <statement> ::= <empty> | <comment line> | <assignment statement> |
> > <identifier>
> >
> > <empty ::=
> >
> > <comment line> ::= # <anything but EOL> <EOL>
> >
> > <assignment statement> ::= <identifier> = <right side>
> >
> > <right side> ::= <identifier> | <identifier list> | <number> | <number
> > list>
> >
> > ........
> >
> > <EOL> ::= <CR> <LF> | <CR> | <LF>
> >
> > <SEP> ::= <SPACE>  | <TAB> | <EOL> | "+"
> >
> > <SPACE>  :: = " "
> >
> > <TAB>  ::= chr(09)
> >
> >
> > etc. etc.
> >
> >
> >
> > regards: Janne.
>
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