[erlang-questions] Strings as Lists

Matt Kangas <>
Tue Feb 19 07:00:44 CET 2008


In my humble opinion, as an Erlang outsider (imo)...

> Principle 5:
> 	RUN IT UP THE FLAGPOLE AND SEE IF ANYONE FAINTS.

Absolutely. :-)

> Principle 4:
> 	LET A HUNDRED SCHOOLS CONTEND.


Erm... are you the one now expressing PERL envy? :-) One of Perl's  
mottos, after all, is: "There's more than one way to do it."

I think there is value in providing *one obvious solution* to a  
problem. If it solves > 90% of common use-cases, is syntactically  
simple, and easy to use in the default configuration, then it's  
probably worth considering. The value here is not total expressive  
power, but instead the likelihood of adoption by users, and thus  
likelihood of solving real, in-the-wild problems.

(Yes, this is the standard "Zen of Python" retort to Perl mongers.)

I'm fascinated by the flexibility you propose, but confused about the  
implications. Should we need to support a Tower of Hanoi for  
notations? How likely are users to ever embed > 1 notation? > 2?

--Matt

On Feb 18, 2008, at 10:55 PM, Richard A. O'Keefe wrote:

> On 19 Feb 2008, at 3:49 am, Joe Armstrong wrote:
> [expressing PERL envy, basically].
>>
>
>> To me, embedding regexps, LaTeX etc. in strings is painful and I make
>> loads of mistakes forgetting to quote things.
>
> Patient:	Doctor, it hurts when I do <this>.
> Doctor:		Then don't do that.
>
> We've had essentially this discussion before.
> I'm reminded of the classic design botch in SGML.
> XML has		<![CDATA[...]]>
> in which the only special characters are the "]]>" ending quote,
> the others being taken literally.  Too bad if you want to nest them!
> SGML also has	<!ELEMENT tag - - CDATA>
> which lets you use <tag>...</tag> to quote the characters ... *and*
> to put a wrapper around them.  It would be perfect for quoting bits
> of SGML in tutorials except that (here comes the botch): it is closed
> by *any* end-tag, not just the one it started with.
>
> There really is no programming language which handles "textual things
> inside
> textual things" terribly well.  The quoting and meta-quoting stuff
> ends up
> being pretty nasty no matter what you do.  The specific proposal Joe
> made
> just now
> 	- would make life horrible for editors like Emacs
> 	- would make things very confusing for people
> 	- would STILL be hard to use.
>
> So, in the light of the old joke, let's not do that.
>
> Principle 1:
> 	NO NESTING.
> 	I love nested blocks, and have since Algol 60.
> 	I love nested expressions, and have since Lisp.
> 	But when you want to combine multiple notations, as for example
> 	XSLT (hiss, spit) does, nesting is for the birds.
> 	I would have called this ONE HEADACHE AT A TIME, but cannot see
> 	how to get by with fewer than two.
>
> Principle 2:
> 	NAME AND CONQUER.
> 	If it's big enough to be a problem, it's big enough to have a name.
>
> Principle 3:
> 	WHAT I SEE ISN'T WHAT HE GETS.
> 	In order to be used in Erlang programs, a notation has to be accepted
> 	by the Erlang tool chain, but it does not have to be part of the  
> Erlang
> 	language or understood by the Erlang compiler.  We have already
> 	accepted this idea for Yecc and Leex.  Keeping it out of the compiler
> 	is also suggested by the next principle:
>
> Principle 4:
> 	LET A HUNDRED SCHOOLS CONTEND.
> 	It's most unlikely that we'll come up with the right design, or even
> 	the right *kind* of design, on the first pop.  Maybe the right way to
> 	do it is to write all our code in Microsoft Word (hiss, spit,  
> screech,
> 	jump, claw!) using styles to distinguish one reading of the text from
> 	another.  Maybe we should be using an SGML-based or XML-based markup
> 	language (not entirely unlike the one I proposed some years ago,
> 	perhaps) with something like Amaya as our editor.  Maybe we should be
> 	asking the aliens from Zeta Reticuli to do our programming for us.
>
> Principle 5:
> 	RUN IT UP THE FLAGPOLE AND SEE IF ANYONE FAINTS.
>
> Here's a sketch of something that can handle large chunks of text in
> a mixture
> of notations.  The key ideas are
> 	- there are Notations (hmm, haven't I heard that before, oh yes, it
> 	  was SGML...).  A Notation provides a rule for quoting interpolated
> 	  text, and may also be associated with a syntax checker.
> 	- there is interpolation, of two kinds.  In the case of Literal
> 	  interpolation, a string in any notation is interpolated as literal
> 	  data according to the Notation's rule.  In the case of Interpreted
> 	  interpolation, a text in one notation may be interpolated in text
> 	  of the same notation only, the result being subject to the syntax
> 	  check of the notation, if any.
> 	- @id@	indicates literal interpolation
> 	  @@	is a plain @
> 	  %id%	indicates interpreted interpolation
> 	  %%	is a plain %
> 	  %\n	is removed; it's continuation.
> 	  These characters were chosen to be minimally obtrusive in LaTeX
> 	  and regular expressions and Erlang text.
> 	- Text chunks have names, which can be used in Erlang code.
> 	- Text chunks may have arguments.
>
> <text definition> ::=
> 	<function name> '(' [<arguments] ')' ['/' <notation name>] 'is' '\n'
> 		<data line>*
> 		'.' '\n'
> 	<data line> ::=
> 		<one white space character> <data item>* ['%'] '\n'
>
> 	<data item> ::=
> 		'%' <expr> '%'
> 	    |   '%' '%'
> 	    |   '@' <expr> '@'
> 	    |   '@' '@'
> 	    |   [^%@\n]
>
> 	<expr> ::=
> 		<variable>
> 	    |   <function name> '(' [<expr> {',' <expr>}] ')
>
> The set of notations we'd need has yet to be determined,
> but it would certainly include
> 	latex
> 	regexp
> 	xml
> 	string		(" and \ are special)
> 	atom		(' and \ are special)
> 	url		(\ is illegal)
>
> Example:
> 	time()/regexp is
> 		^1?[0-9]:[0-5][0-9] [AP]M$
> 	.
> 	explanation()/latex is
> 		The regular expression \verb|@time()@| matches
> 		any string of the form
> 		\textit{h}:\textit{m}\verb*| |\textit{ampm}
> 		where \textit{h} is one or two decimal digits,
> 		representing an hour 1--12, \textit{m} is two
> 		decimal digits, with a leading zero if necessary,
> 		representing a minute 00--59, and \textit{ampm}
> 		is either AM (\textit{ante meridiem}) or
> 		PM (\textit{post meridiem}).\foot{For the pedants
> 		amongst you, note that it is meridiEM, not
> 		meridiAN}
> 	.
> 	base()/url is
> 		http://erlang.example.org/%
> 	.
> 	relative()/url is
> 		erlang/doc/preproc/hundred.html%
> 	.
> 	complete()/url is
> 		%base()%%relative%%
> 	.
> 	omnium_gatherum() is
> 		{@time()@()@()@}%
> 	.
>
> A preprocessor would turn this into plain Erlang.
>
> There isn't actually much, if anything, in this that is specific to
> Erlang.

-- 
Matt Kangas
 – www.p16blog.com




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