Is it possible to combine til with a variable?

[don]

For example the following codedouble:{x*2}til (double 5)prints 0...9Suppose I wish to dotil zUntil double z > 20How would I express this in Q?

[trieder]

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You can't combine til with an expression like that. I think you can do somet=
hing like that with Haskell though.

The closest thing I can think of would be something like:

a@:where(a:double til 1000)>20

You could also use a loop and dynamically build an expression, but that woul=
d be "illegal," slow and ugly.

[don]

Thanks Tim, is there a way to do lazy evaluations of lists? The
following crashes the system which indicates it is unnecessarily
iterating over everything (i.e. it wold be nice to break on the first
false)

double:{x*2}
a@:where(a:double til 1000000000)<20
a

[charlie]

could cook your own til

q)mytil:{-1_(1+)\[{x>y z}[x;y];0]}

q)mytil[20;double]

0 1 2 3 4 5 6 7 8 9

doesn't scale well though. 🙂

[trieder]

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No lazy eval in q except on file reads (mmap) as far as I'm aware.

Take a look at this for a conditional break:

https://code.kx.com/trac/wiki/Reference/BackSlash#iterate