This is the story of what happened when I went down a rabbit hole.
It starts with k7. If you press Ctrl-] in the k7 WASM console, this appears:
x^x*/:x:2_!100
That's a prime number filter. There are faster ones - kparc.com's x,1_&&/80#'!:'x is beautiful - but this one is really short.
| # Unevaluated | |
| A `wrap attribute that causes overindexing to auto-mod based on length of list. | |
| Avoids mismatch of behaviour of i# and -i#. Cut will auto-fill if not long enough. | |
| Negative indexing wraps backwards: (`wrap"abc")[-1] is "c" | |
| Requires `null to go back to default behaviour? | |
| ## Slice as basis for lots of primitives | |
| Inspired by ngn's https://chat.stackexchange.com/transcript/message/59004538#59004538 ... |
It's 2020, and there's now many ways to work with data of arbitrary length in Excel:
But if you use or support older Excel versions, VBA can still be useful.
Thought experiment:
Which k primitives can be implemented as k-strings, reasonably efficiently, with a handful of 'native' built-ins?
Not verified to be in dependency order yet... may depend on the choice of 'fundamental' primitives. Need to do speed tests too.
k9 syntax (download via Shakti). Got a better way to write one? Feel free to comment, you'll be credited!
Current in k9 2020.03.27.
Standard lookup:
[a:1;b:2]`b
2
Mildly interesting results from string analysis of a handful of k files. If you have more public k files or suggestions for further analysis, comment below!
This uses the latest Shakti.
Corpus:
In The APL Orchard, ngn said:
the or-dot-and [∨.∧] trick is one of the most beautiful apl expressions ever, worth staring at :)
Well I had better learn it then...
Apparently it computes a transitive closure of a binary relation. Let's hit Wikipedia.
| / Abstraction considered harmful? One-at-a-time thinking preventing parallelisation? | |
| / AoC 2019 problem 4 | |
| ```q | |
| i:${x+!1+y-x}.`i$"-"\:"193651-649729" | |
| / Results are the same: | |
| 1~({x~^x}#i)~i@&&/~<':+i | |
| / But the second line (Attila's) is much faster: |
| / "Apter trees" http://archive.vector.org.uk/art10500340 | |
| / https://github.com/stevanapter/hypertree#concepts | |
| / http://nsl.com/k/treetable/treetable_k3.html | |
| / http://www.nsl.com/k/trees.k | |
| / John Earnest notes https://github.com/JohnEarnest/ok/blob/gh-pages/docs/Trees.md | |
| / Aaron Hsu talk on high-performance tree wrangling https://www.youtube.com/watch?v=hzPd3umu78g | |
| / https://www.dyalog.com/uploads/conference/dyalog18/presentations/U19_Tree_Wrangling_the_APL_Way.pdf | |
| / Translation into k by JE: https://github.com/JohnEarnest/ok/blob/gh-pages/examples/key.k | |
| / Conquering recursion: http://archive.vector.org.uk/art10501740 | |
| / https://news.ycombinator.com/item?id=21680133 - comments from geocar and John Earnest |
| // https://twitter.com/ua6oxa/status/1170457046153650176 | |
| "use strict"; | |
| function evalInContext(env, code) { | |
| const | |
| s = JSON.stringify, | |
| locals = Object.keys(env), | |
| keys = locals.map(function(k){return s(k)}), | |
| values = locals.map(function(k){return env[k]}), | |
| body = s("return eval(" + code + ")") |