Mailing List Archive: Re: Parsing with 2 conditions

[REBOL] Re: Parsing with 2 conditions

From: richard:coffre:francetelecom at: 10-Apr-2002 14:14


Thanks a lot for this complete explanation. It's clear now.

-----Message d'origine-----
De : Brett Handley [mailto:[brett--codeconscious--com]]
Envoy=E9 : mercredi 10 avril 2002 12:05
=C0 : [rebol-list--rebol--com]
Objet : [REBOL] Re: Parsing with 2 conditions

Bonsoir,

> The following instruction works :
>   if parse/all ligne [thru "Symbol" to end]
> why the next one doesn't work :
>    if parse/all ligne [ "Symbol" ]

First let's look END. END is like asking the question "Are we at the end?"

    >> parse/all {} [end]
    == true
    >> parse/all {x} [end]
    == false

In these cases, ["Symbol"] is the same as ["Symbol" END]:

    >> parse/all {} []
    == true
    >> parse/all {} [end]
    == true
    >> parse/all {x} []
    == false
    >> parse/all {x} [end]
    == false
    >> parse/all {x} ["x"]
    == true
    >> parse/all {x} ["x" end]
    == true

["Symbol"] is like "Is there a 'Symbol' here?"

    >> parse/all {Symbol} ["Symbol"]
    == true
    >> parse/all {xSymbol} ["Symbol"]
    == false
    >> parse/all {xSymbol} ["x" "Symbol"]
    == true
    >> parse/all {xSymbol} [skip "Symbol"]
    == true
    >> parse/all {Symbolx} ["Symbol"]
    == false

TO ... Is like saying "Keep going until you reach...":

    >> parse/all {abcdef} [to "d" "def" end]
    == true
    >> parse/all {abcdef} [to "e" "ef" end]
    == true

THRU ... Is like saying "Keep going until you reach the end of ..."

    >> parse/all {abcdef} [thru "e" "f"]
    == true
    >> parse/all {abcdef} [thru "ef"]
    == true

SKIP -  "Advance by one position"

    >> parse/all {abcdef} [to "e" skip "f" end]
    == true

TO END is like "Keep going to the end"

    >> parse/all {x} [to end]
    == true
    >> parse/all {xxxxxx} [to end]
    == true
    >> parse/all {x} [to end "x"]
    == false

So after all that

    [thru "Symbol" to end]

is like saying

    "Keep going until you reach the end of 'Symbol'
    (that is - after the 'l'), and then keep going to the end."

Whereas

    [ "Symbol" ]

is simply like saying

    "Is there 'Symbol' right here, and if is advance throught it.
    Are we now at the end?"

> 2nd question :
> I have the instruction "if parse/all ligne [thru "Symbol" to end]" to look
> for the word Symbol in a string. How can I do to look for Symbol and Frame
> at the same time ?

    >> parse/all {xxxSymbolxxx} [thru "Symbol" to end]
    == true
    >> parse/all {xxxFramexxx} [thru "Symbol" to end]
    == false
    >> parse/all {xxxFramexxx} [ [thru "Symbol" | thru "Frame"] to end]
    == true

Also have a look at:

    http://www.codeconscious.com/rebol/parse-tutorial.html

I hope this helps.
Brett Handley.