Hi Bart, thank you for considering my question! Indeed, what I wrote was
perhaps
misleading. Giving the example
(((a OR b) OR c) AND d)
I meant the result of translating the AST into text in a "canonical way", that
is, writing this concatenation:
formula "R"
: ^(operator ldefOperand rightOperand) => this string: openBracket +
leftOperand + closeBracket + operator + openBracket + rightOperand +
closeBracket
I suppose a deep tree created as sketched in the previous posting, that is, by
the scheme
: operand (operator^ operand)*
can be safely translated by applying the rule given above ("R") recursively. So
far, so good. But the brackets are superfluous unless the current operator has
a
lower precedence than the operator in the "context", the tree level of which
the
present operand is a child. For example, this input
A + B + C + D + E + F
generates
(((((A + B) + C) + D) + E + F)
So my question amounts to: is it a good idea to accomplish the translation in
these steps:
a) build the AST in the standard way (meant for operation execution), creating
a
deep tree with one inner node per operator
b) serialize it using an adapted form of "R", which uses or omits the brackets
dependent on a rule parameter providing the context operator
? Or should one build the AST differently, namely, making the top-level
operands
of an operator the children of the operator, like:
^('+' A B C D E F)
Thank you, and kind regards
-- Hans-Juergen
________________________________
Von: Bart Kiers <[email protected]>
An: Hans-Juergen Rennau <[email protected]>
CC: "[email protected] interest" <[email protected]>
Gesendet: Montag, den 9. Mai 2011, 16:16:53 Uhr
Betreff: Re: [antlr-interest] Translating expressions - advice?
Wait I think I misunderstood. Your example `(a OR (b OR (c AND d)))` is just an
example expression, right?
In that case, yes, these parenthesis are part of the token stream, but if you
apply rewrite rules (or AST operators `^` and `!`) properly, these parenthesis
are easily removed from your parse tree.
See: http://www.antlr.org/wiki/display/ANTLR3/Tree+construction
or:
http://stackoverflow.com/questions/4931346/how-to-output-the-ast-built-using-antlr
Regards,
Bart.
On Mon, May 9, 2011 at 4:10 PM, Bart Kiers <[email protected]> wrote:
I get the impression you think that when creating AST's, ANTLR inserts
parenthesis (brackets). This is not the case: I guess what you're seeing is
just
the tree's `toStringTree()` that displays these parenthesis to make the
hierarchy of the tree apparent.
>Or am I misinterpreting your question?
>
>
>Regards,
>
>
>Bart.
>
>
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