Hi Albert,
thanks for your answer. It helped in some other issues I have.
I did experiment with parenthesis, but obviously not in the right place.
I found the filterA arrow to do the thing I want, like this:
getRowWithHeading caption =
filterA (deep (hasName "th" /> hasText (==caption) )) />
hasName "td" >>>
getChildren
I like to ask you if you might know the answer to the following:
In a structure
+---XTag "a"
| +---XText "A text 1"
|
+---XText "Plain text 1"
|
+---XTag "a"
| +---XText "A text 2"
|
+---XText "Plain text 2"
...
I must combine "A text 1" with "Plain text 1", etc., but they are in sequence on
the same level.
Is it possible, in a simple way, to do it in a single arrow flow?
(Or only outside the arrow by pairing the list items?)
Something like:
hasName "a" /> getText &&& (getNextItem??? >>> getText)
I assume not, but I'm still new to Haskell and would like to check.
br,
vlatko
Original Message
Subject: Re: [Haskell-cafe] Problem with HXT `when`
From: Albert Y. C. Lai
To: haskell-cafe@haskell.org
Date: 25.09.2013 03:22
On 13-09-21 05:13 AM, Vlatko Basic wrote:
I'd like to extract A texts from row with header "Caption", and have
come up with this
runX $ doc
>>> (deep (hasName "tr") --
filter only TRs
>>> withTraceLevel 5 traceTree --
shows correct TR
`when`
deep (
hasName "th" >>>
-- filter THs with specified text
getChildren >>> hasText (=="Caption")
) -- inner deep
>>> getChildren >>> hasName "td" -- shouldn't here be only
one TR?
>>> getChildren
)
>>> getName &&& (getChildren >>> getText) -- list has TDs
from all three TRs
Operator precedences:
>>> infixr 1
`when` infixl 9 (default)
Therefore, this expression redundantly parenthesized and systematically indented
to ensure that you are on the same page with the computer is:
runX $
doc
>>>
( deep (hasName "tr")
>>>
-- begin{conditionally prints but otherwise is arr id}
( withTraceLevel 5 traceTree
`when`
deep ( hasName "th"
>>>
getChildren
>>>
hasText (=="Caption")
) -- inner deep
)
-- end{conditionally prints but otherwise is arr id}
>>>
getChildren
>>>
hasName "td"
>>>
getChildren
)
>>>
( getName &&& (getChildren >>> getText) )
The condition on Caption ends up controlling trace messages only; it is
not used to limit real processing.
"when" doesn't help even when used correctly: it doesn't ban data. "guards" and
"containing" ban data, but you have to put them at the right place, i.e.,
parenthesize correctly.
runX $
doc
>>>
( deep ( hasName "tr"
`containing`
deep ( hasName "th"
>>>
getChildren
>>>
hasText (=="Caption")
)
)
>>>
getChildren
>>>
hasName "td"
>>>
getChildren
)
>>>
( getName
&&&
(getChildren >>> getText)
)
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