APL\iv: an APL interpreter and stream processor written in Go

by chrispsn • 7 years ago

143 27 7 years ago

$Preview of APL\iv: an APL interpreter and stream processor written in Go$ github.com

nemo16183• 7 years ago

Fun fact: All three of Go's creators have written APL interpreters, and Go's "iota" keyword is modeled after the corresponding APL operator.

boomlinde3• 7 years ago

I wouldn't say that Go iota is modeled after APL iota. They share the same name, but that's really where the similarities end. The iota operator in APL is more like the unary case of the python range function.

nemo16183• 7 years ago

They are both used to generate a sequence of consecutive integers, although Go's iota starts at 0 whereas APL's starts at 1.

"Ken suggested iota for the counter and, since all three of us (Ken, Robert, Rob) had implemented APL interpreters, it seemed a perfect thing to us." - Rob Pike

kasbah3• 7 years ago

Rob Pike also implemented an APL-like big number calculator in Go more recently: https://github.com/robpike/ivy

The author has never used APL. It's a chicken and egg problem. (...) All testing has been done with tryapl.org.

There are also a few free software implementations of APL most notably GNU APL. I have been sticking to that while learning APL. https://www.gnu.org/software/apl/

threwawasy12282• 7 years ago

I've personally found GNU APL to be a bit flimsy, and not some of the design choices they made in it to be a bit odd. It also deviates from the ISO standard, if that matters to you.

Dyalog is the only implementation that is robust and production ready that is still actively maintained. I would suggest learning with something other than the GNU implementation.

3xblah• 7 years ago

Of course it takes less time and effort to write an APL interpreter than it does to actually learn APL.

I wish there were more languages like that.

segmondy• 7 years ago

Every programmer should implement 6 languages assembler, basic, c, lisp, prolog & APL.

4thaccount2• 7 years ago

Forth?

gaius• 7 years ago

Disclaimer

The author has never used APL

I’d like to know more about the underlying motivation! APL is a fascinating language but I’m not sure how you’d implement it efficiently in a language like Go - you would need intrinsics to get at the vector instructions no?

kd0amg• 7 years ago

Even without vector intrinsics, you can get a lot of mileage out of spending almost all your time in loop bodies that map primitive operations over large arrays. Interpretive overhead tends to grow a lot slower than the user program's input size.

pvitz• 7 years ago

IIRC J didn't use intrinsics until maybe two years ago. They used mostly C and everything was built with for-loops. Some special verbs or phrases were however implemented in x86 assembly.

jerf• 7 years ago

Go assembler can get to vector instructions, for instance as used by Cloudflare to implement crypto speedups: https://blog.cloudflare.com/go-crypto-bridging-the-performan...

grumpydba• 7 years ago

Indeed but without intrinsics, functions using those vector instructions cannot be inlined, and the go calling convention's overhead is still big.

patrickg_zill• 7 years ago

I think part of the speed of APL is the way that parts of it are small enough to fit in L2 cache (at least 1 of the APL descended languages, Q / K, bragged about this). Whether the Go implementation seen here will fit in typical caches of today's CPUs I don't know.

jim-jim-jim• 7 years ago

A bit tangential, but what do people here use to input APL characters in macOS?

I've been using Dyalog's GUI, but I'd much rather be using free software from the usual terminal. It'd be nice if there were just a global input method like the ones they have for human languages.

i_don_t_know• 7 years ago

Follow the instructions at https://www.dyalog.com/apl-font-keyboard.htm

Then add another input method for APL as you would for switching between English, German, French, etc keyboard layouts.

kwhitefoot• 7 years ago

Slightly off topic: what might this or any other APL interpreter be used for in what one might call mainstream business or technical applications?

APL\iv: an APL interpreter and stream processor written in Go

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