From: Dan Zwell <dzwell@...>
Date: 2007-04-30T05:03:14+09:00
Subject: Re: Infix to Postfix Method

Thomas Hurst wrote:
> Demo:
>   # Token stream
>   irb(main):009:0> toks = analyser.simplify(tokenizer.tokenize("foo AND bar OR (wibble OR wobble NOT foo)"))
>   [#<NSearch::SubStringQuery:0x18a4a20 @substr="foo">,
>    :and,
>    #<NSearch::SubStringQuery:0x18a49f8 @substr="bar">,
>    :or,
>    :open,
>    #<NSearch::SubStringQuery:0x18a49a8 @substr="wibble">,
>    :or,
>    #<NSearch::SubStringQuery:0x18a4958 @substr="wobble">,
>    :and,
>    :not,
>    #<NSearch::SubStringQuery:0x18a4908 @substr="foo">,
>    :close]
> 
>    irb(main):010:0> analyser.rpnise(toks)
>    [#<NSearch::SubStringQuery:0x188a670 @substr="foo">,
>     #<NSearch::SubStringQuery:0x188a648 @substr="bar">,
>     :and,
>     #<NSearch::SubStringQuery:0x188a5f8 @substr="wibble">,
>     #<NSearch::SubStringQuery:0x188a5a8 @substr="wobble">,
>     #<NSearch::SubStringQuery:0x188a558 @substr="foo">,
>     :not,
>     :and,
>     :or,
>     :or]
> 
> You can then follow the instructions, popping each SubStringQuery onto a
> stack and popping them off on :and, :or and :not to build a tree of
> query objects:
> 
> #to_s
>   OR(OR(AND(NOT("foo"),"wobble"),"wibble"),AND("bar","foo"))
> 
> #to_sql
>   (((NOT (Title LIKE "%foo%") AND Title LIKE "%wobble%") OR Title LIKE
>     "%wibble%") OR (Title LIKE "%bar%" AND Title LIKE "%foo%"))
> 
> 
> I'd recommend against using Ruby's own Generator, btw; it uses callcc
> and has a tendancy towards being slow and leaky.  If you just need a
> #next/#peek method, just turn it into an array and shove it in an
> appropriate object which tracks the position.
> 

That's pretty neat. I hadn't thought of using this stuff to generate 
SQL. I'll probably acually use that idea some day. And thanks for the 
bit about Generator. I'm currently looking through a computational 
script (ported from c++)--I could never figure out why it used all my 
ram within a few seconds, but it used Generators several thousand times. 
I'm rewriting parts of it now, and we'll see what happens.

Dan