[stringtemplate-interest] List comprehensions Was Re: Working with filtered list

[Terence Parr]

On Jun 26, 2007, at 7:11 PM, John Snyders wrote:
> Here is what it might look like
> $[x for x in data if x.IsSmart]:{ $it.CustomerName$ }$
>
> No comparison expressions have been introduced. The program is still
> responsible for implementing the logic by setting the IsSmart  
> property.
> It is just a combination of list iteration, if evaluation (the same if
> already supported), and list construction.

That is the same as

$data:{ d | $if(d.isSmart)$$d.CustomerName$$endif$}$

right?  The list comprehension syntax is nicer though.

> List construction already allows a comma separated list of  
> expressions.
> So something like this is possible:
> $[items, decorate("foo"), "bar"]: { x | ($x$)};separator="; "$
>
> If it allowed templatesExpresson (this includes the syntax for
> iterating) then something like this would be allowed:
> $[items:decorate(it), decorate("foo"), "bar"]: { x | ($x 
> $)};separator="; "$

Ooops...that doesn't work?  It should handle any expression.

> All that would be needed to have the power of Python list  
> comprehensions
> is fitting in the "if" expression. Perhaps:
> $items if it.isFancy :decorate(it)$
> or
> $items : { x | x.isFancy | Fancy: $x$. }$

Well, we can already do this now, just less beautifully as we need  
the if/end.

> On the other hand I wonder if the Python list comprehension syntax is
> more power full.

Technically, probably not.  I would have to think harder.


Ter