Reporting system - declarative

[Hendrik Boom]

On Sat, 09 Jul 2011 18:05:48 -0400, Yawar Amin wrote:

> Hi John,
> 
> On 2011-07-08, at 23:33, John Ralls wrote:
> 
>>> […]
>> 
>> Fun. Two questions: Can that be easily converted into a string parser
>> so that normal users aren't put off by the extra parentheses,
> 
> I guess we could replace all the parens with more HTML-reminiscent
> characters like << and >>, so you’d get stuff like (btw I’m using dots
> to represent spaces everywhere as my MUA is eating up the first blank
> space on every line):
> 
> <<report ...
> ..<<defs
> ....<<def-date ...>>
> ....<<def-date ...>>
> ..>>
>>>
>>>
> then do a search-and-replace to turn that back into Scheme. We might
> overcome a lot of phobia if we hide the fact that we’re really making
> them write Scheme :-)

There's also the use of [ ] in the old much-forgotten Lisp 1.5 
metalanguage -- using foo[a, b, c] instead of (foo a b c).  Perhaps foo[a 
b c] would suffice.  And C uses context-prefixed curly brackets, as in do
{ ... } and else{ ... }.

> 
> Another thing we could recommend is lining up the parens below the
> function names on multi-line function calls. I mean:
> 
> (report ...
> ..(defs
> ....(def-date ...)
> ....(def-date ...)
> ..)
> )
> 
> In the beginning I found it a lot more digestible when I didn’t have to
> deal with the mess of ‘)))))))’.

I still find your layout more digestible, after years or using Scheme-
related languages.  I prefer it in C with its curly brackets, too.  

Now the parentheses in List are a syntactic price that's paid to make the 
metaprogramming aspects more modular.  There's no question of what can 
fit within what, as there would be with independent pieces of context-
free grammar.  I consider uniform means of reducing the parentheses 
problem a boon.  
In my own Lisp dialect I used an additional convention:  '/' in a list 
signals the start of a sublist as its last element; thus ( a / b ) is 
equivalent to ( a ( bb )), and ( a / b / c ) equivalent to ( a ( b ( c 
))).  This eliminated most of the closer-clusters.  It ended up having a 
role similar to the that of ';' in other programming languages.  
Unfortunately, '/' and ';' now have other, incompatible meanings in 
Scheme.

But most Scheme programmers object to any suggestion that brackets are a 
problem for Real Programmers, as if methods of dealing with parentheses 
attack their virility or something like that

I just think programs should be written in a manner that makes them as 
clear as possible.  Programming is hard enough without unnecessary 
obfuscation.

> 
>> and is there anything about that that works in Scheme but not in C?
> 
> I really, really don’t want to deal with memory management….
> 
> Anyway, I kind of mercilessly hacked the ‘Hello, World’ report that
> comes with GC, in
> share/gnucash/guile-modules/gnucash/report/hello-world.scm, and wrote a
> few functions which do what I was talking about. So now I’m able to say:
> 
> (d:report
> "income-statement" ; name
> 0 ; defs
> ; Have to keep this title while experimenting in the sample report that
> ; comes with GnuCash
> "Hello, World" ; title
> "2011-01-01 to 2011-07-31" ; subtitle (d:filter-none ; body

Is there a missing line break in this line?

>   (d:p "Some text.”)
>   (d:p "A little more text.")))
> 
> … and that generates the report that you’d expect. The ‘d:’
> (‘declarative’) prefix is just to make sure I don’t clash with anything.
> Code is up on https://github.com/yawaramin/gc-decl-reports (I'm not
> pushing anything which causes a crash for me, so it should be reasonably
> safe. But caveat emptor).
> 
> Regards,
> 
> Yawar
> 
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