Alex,
I see your point and that was my first thought also. After sleeping on it, what I am really suggesting now is not "breaking apart" the repeat structure as much creating an new sequential access method operator(s). This is more flexible than tying it to the loop operator. It means that you have complete control over the separate items and can make them out of sync on purpose (it might even be nice to be able to specify a starting point instead of creating a new chunk --kind of like the skip n lines in a search. For instance, you want to match every line in A with every other item in B. It just happens to be a quirk that the pointers are currently embedded into the repeat for each structure. This would also significantly simplify the possible syntax variations in the repeat structure.
The access each line X and the next access X would be paired. Help me out. How can this be specified so that it makes sense for the language? It would have interleave the block structure to be useful.
Access each line X in arrayX from line 3 --just creates the pointers and access mode structures
do something
next access X --grabs X and advances the line pointer
end access X --destroys the pointer structure?
I would also like it applied to Arrays if the order they come out is deterministic --like the order they were created, or numeric order of a numeric key.
And yes, I am all for making the language more readable --self documenting. After all that is one of the points of X-Talk.
Dennis
On Apr 13, 2005, at 11:25 AM, Alex Tweedly wrote:
Dennis Brown wrote:
The Idea is to break apart the essential functional elements of the repeat for each control to allow more flexibility. This sample has a bit more refinement than what I posted yesterday in Bugzilla.
The new keyword would be "access" , but could be something else.
An example of the use of the new keywords syntax would be:
access each line X in arrayX--initial setup of pointers and X value
access each item Y in arrayY --initial setup of pointers and Y value
repeat for number of lines of arrayX times --same as a repeat for each
put X & comma & Y & return after ArrayXY --merged array
next line X --puts the next line value in X
next item Y --if arrayY has fewer elements than arrayX, then empty is supplied, could also put "End of String" in the result
end repeat
Another advantage of this syntax is that it provides for more flexibility in structure of loops. You could repeat forever, then exit repeat when you run out of values (based on getting an empty back). The possibilities for high speed sequential access data processing are much expanded which opens up more possibilities for Revolution.
Dennis,
I think having more flexible repeat structures to allow parallel passes through lists or arrays is a really good idea, but I don't like the form you have suggested. It seems wrong to have separate statements to setup the loop; as far as I know, the language currently keeps the meaning of each statement self-contained, so I think this multi-line form would be a hard one to "sell".
I think it would be better to add a new keyword to indicate parallel looping; the primary loop determines the repeat-termination test criterion, while the others are incremented/advanced in synch. (of course, using exit allows you to terminate the loop based on the secondary loops if needed).
I'd suggest the word "also" since it's not currently used, or perhaps the phrase "also each".
So the form would be something like
repeat for each line X in xList also item Y in yLine repeat for each line X in xList also each item Y in yLine repeat for each line X in xList and also each item Y in yLine
and of course there could be more than 2 :
repeat for each line Y in ylist also line x in xlist also item z in zlist also item name in namelist ...
This would allow the variants
repeat forever also each item Z in theList repeat for each element E in myArray also each line X in xList repeat with i = 1 to 100 also each line X in xList
etc.
And for symmetry, it might also be feasible to allow
repeat for each X in Xlist also i = 1 step 1
(since there's not a terminating condition in the secondary, it would confusing to have i = 1 to 100, so simply specify initial and step values).
Similar to this, I'd love to see a method for accessing arrays which gives both the key and the element. Currently, you can say
repeat for each line K in the keys of myArray
put myArray[k] into V
but most modern languages have something like
for (k,v in myarray)
which gives both key and value without needing to do another hash lookup.
And now that I'm started on this topic, I've always envied the readability of Python's tuple-assignment. I find
x1,y2,x2,y2 = myRectangle
much more obvious than
x1 = myRectangle[0]
y1 = myRectangle[1]
x2 = myRectangle[2]
etc.
In Transcript, I really wish I could say put myRectangle as items into x1,y1,x2,y2 or put the items of myRectangle into x1,y1,x2,y2 instead of the clumsy put item 1 of myRect into X put item 2 of myRect into Y etc.
No performance advantage - but so much more readable.
-- Alex Tweedly http://www.tweedly.net
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