[Ur] Hamlet like XML, structured by indentation with tag autoclosing

[Gabriel Riba]

Correction:

El 18/06/15 a les 23:55, Ziv Scully ha escrit:
 > As far as I can see, the proposed changes do 3 things:
 >
 > (1) Add a few new things especially for layout (the forall/foreach/etc.
 > sort of thing).
 > (2) Make normal XML a bit nicer by eliminating closing tags.
 > (3) Make XML mixed with Ur/Web "macros" less clunky by eliminating some
 > extra {} and <xml></xml> pairs.
 >


* First, with structure by indentation with tag autoclosing, the 
document tree structure shows clearer. (Your (2))

Check https://hackage.haskell.org/package/hamlet
and 
http://www.yesodweb.com/book/shakespearean-templates#shakespearean-templates_hamlet_html

----------------

* Second, you can specify conditional subtrees, subject to decision 
logic, making nested xml nicer (Your (3))

   $if {cond}
      subtree1

   $elsif {cond}
      subtree2

   $else {cond}
      subtree3

----------------

* Third, you can specify foldMap traversals of foldable containers

    $foldmap {items_expr} <| {item_pattern}

       item_subtree embedding {[item_patt_var]}


Haskell differentiates between sequentially enforced traversal 
(Data.Traversable) and non-enforced (Data.Foldable) as 
non-monadic/applicative code exec. order is not granted sequential.

I am not sure about this need in Ur, but in case, an extra logic 
statement could be used.

Other logic statements:

------------------

$case {expression}
$of {pattern}
     subtree1 embedding {[patt_var]}

$of {pattern}
     subtree1 embedding {[patt_var]}

------------------

$some {option_expression} <| {pattern}
     subtree1 embedding {[patt_var]}

$none
     subtree2