Re: introduction to BNF, concrete syntax trees

On 25 Sep 2006 01:16:28 -0400, markww wrote:


> I'm just starting to look at BNF. I have to take a simple expression
> like:
>
> (A + B * C) * D
>
> and create a concrete syntax tree of it. Before I start writing my
> application to parse the above, I need to understand how to do this on
> a piece of paper. My first thought is to tokenize (by whitespace) every
> component of the statement, then label its type. I have 3 types to
> choose from:
>
> f = factor
> t = term
> e = expression
>
> with the following rules:
>
> expression ::= exp "+" exp |
> exp "-" exp |
> term
>
> term ::= term "*" factor |
> term "\" factor |
> factor
>
> factor ::= number |
> identifier |
> "(" expression ")"


There could be other ways to classify lexical tokens of an expression. For
example:


<expression> ::=
      <prefix><operand><postfix>[<infix><expression>]


<prefix> ::= <prefix>[<prefix>]
<postfix> ::= <postfix>[<postfix>]


<prefix> ::= <unary> | <left-bracket>
<infix> ::= <dyadic> | <left-index> | <comma>
<postfix> ::= <unary> | <right-bracket>


Also, priorities and association need not to be necessarily handled on the
grammar level. See, for further information:


http://www.dmitry-kazakov.de/ada/components.htm#7.2


--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

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