World: r3wp
[Parse] Discussion of PARSE dialect
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Graham 6-Nov-2008 [2801x2] | If you turn a string into a block and there's something present which is an illegal rebol value ... you get an error. |
Is there a way such values can be turned into a legal type ....and not get an error? | |
BrianH 6-Nov-2008 [2803] | That sounds like unbound words. In R3 unbound words are not an illegal type. |
Graham 6-Nov-2008 [2804x2] | great. |
so if we have words like asdfs@ etc, we don't get illegal email types etc? | |
BrianH 6-Nov-2008 [2806x3] | In R2 you just bind the words to system/words, or LOAD instead of TO-BLOCK. |
That's a different issue, that's illegal REBOL syntax. You are out of luck there. | |
Just don't try to parse illegal REBOL syntax as if it were legal and you'll be fine. You have string parse for non-REBOL strings. | |
Chris 6-Nov-2008 [2809] | Brian, would the above example return true, as the entire string has been matched? Or just work in that it matches the "bc"? |
Graham 6-Nov-2008 [2810] | well, if you have a data input screen ... then the user can enter all sorts of stuff |
BrianH 6-Nov-2008 [2811x5] | Unless that user is trained to enter the right syntax, you'll have to clean up before you can load the string. |
Chris, the above example would not return true. | |
String parse is a good way to clean up input :) | |
Graham, the parser that turns strings of REBOL syntax into REBOL data is LOAD, not PARSE. If you want to clean up those strings or loosen the syntax, LOAD is the function to change. | |
On the other hand, you can write a parser in string PARSE that would read data in whatever format you like. | |
Graham 6-Nov-2008 [2816x3] | I was asking if parsing data could be made easier by altering the way values are turned into rebol types |
>> to-block " @" ** Syntax Error: Invalid email -- @ ** Near: (line 1) @ | |
string parsing is so tedious! | |
BrianH 6-Nov-2008 [2819x2] | Now that is interesting. LOAD and TO-BLOCK do that. It would be interesting to write a set of rules in PARSE that read REBOL syntax and generate REBOL data or warnings instead of errors. For your purposes you might consider LOAD/NEXT in a loop inside of TRY blocks. |
If you write your own handler for structural delimiters to build your own blocks you can use load/next for the simple literal values. | |
Graham 6-Nov-2008 [2821] | Perhaps to block can convert "illegal" values into strings instead of flagging an error? |
BrianH 6-Nov-2008 [2822x2] | Personally, I just prefer string parsing with PARSE, but I'm weird that way. We're trying to make PARSE less tedious though. |
I would rather TO-BLOCK convert illegal values into error values, of the syntax error type. | |
Graham 6-Nov-2008 [2824] | oh well, make it an option for those of us who prefer diffferently |
BrianH 6-Nov-2008 [2825x3] | Not up to me. I think that the decision was that relaxing REBOL syntax was a slippery slope that would lead to uncatchable syntax errors. The syntax error mechanism is one of the most valuable debugging tools we have. You might need to consider the possibility that if what your users are entering isn't legal REBOL syntax, it isn't REBOL syntax and needs a different parser. |
REBOL syntax is weird by user standards. | |
It might be better to come up with a good set of flexible predefined PARSE rules for data entry that can be reused without much trouble by a variety of programmers. That would solve the problem for everyone without making it difficult for REBOL debugging. | |
Graham 6-Nov-2008 [2828] | to-block/relax :) |
BrianH 6-Nov-2008 [2829] | You can't do that. TO-BLOCK is a wrapper for TO BLOCK! val and TO is an action! with a fixed arity. What you want is a parser for user data that isn't in REBOL syntax. That we can do. |
btiffin 6-Nov-2008 [2830] | Graham; I've been trying to convince Carl for this TRANSCODE in R3 doesn't throw syntax errors. |
Graham 6-Nov-2008 [2831] | what's transcode? |
Chris 6-Nov-2008 [2832] | Graham, my 'import (and 'as) function is kindof addresses this. I've also been working on loading non-rebol data (in some cases numbers that use , -- 1,000 or us-style dates mm/dd/yyyy). This'll be even better with some transformational chops in parse... |
btiffin 6-Nov-2008 [2833] | The new LOAD/NEXT |
Graham 6-Nov-2008 [2834x2] | I agree that things should be easier to parse - and that includes preparing data to be parsed. |
Having predefined parse rules is just more stuff to remember. | |
btiffin 6-Nov-2008 [2836] | Oldes? Henrik? Maarten? posted a nice all-value loader for me, its in some of the construction boss code, but I don't have that source ported to this machine yet... I didn't learn anything, as I just cut'n'pasted the snippet. |
Graham 6-Nov-2008 [2837] | any-one! |
BrianH 6-Nov-2008 [2838] | It's not more to remember, it's just a module to load :) |
Graham 6-Nov-2008 [2839] | Can you give me an example of what you are thinking of? |
Tomc 6-Nov-2008 [2840] | the ability to remove/override/extend the set of chars considered "special" in string splitting |
Graham 6-Nov-2008 [2841x2] | like " ? |
some sql dialects have the handy abilty to set the current delimiter | |
Tomc 6-Nov-2008 [2843x3] | the abilitty to "recognize all datadypes not just a frw like integer! tag! in string parsing |
yes Graham quote is one that can be hard to work around or show up unexpectedly | |
comma and space seem to be others | |
Graham 6-Nov-2008 [2846] | block parsing .. you can't match specific integers |
Pekr 6-Nov-2008 [2847] | Graham - there is going to be a LIT keyword to match integers .... |
Tomc 6-Nov-2008 [2848x3] | this may bot be a well formed thought but ... the ability to directly feed a port into parse |
maybe something like | |
parse open txcp://where.ever:555 rule | |
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