Protocol for defining small functions in external binaries

[andychu]

This could be things like a "split" algorithm, uppercase, base64, crypto, etc.

Sort of related to #848 which is about external processes, coprocesses, VMs, containers

Basically we are laying the logical concept of functions on top of external processes

I think it will be a QTT protocol over stdin / stdout, with args as columns of stdin, and return values as columns of stdout. Depends on #827

Now that we have #984 proc signatures, we should make something sort of consistent? Or maybe it will depend on #631 so there is a DSL but no func keyword

define sha256 {
  command = %(myprog.py sha256)
  args {
     ...
  }
  returns {
    ...
  }
}

• then such functions can be used inline like

echo $sha256('foo')
var x = sha256('foo')

and maybe

echo ${myvar|sha256}

for escapers. Related to string safety

And in vectorized form

ls --qtt | cols (sha256 = sha256(foo))

related to #827 as well

[andychu]

This feels a little related to the "standard standard library" problem, i.e. where every language has slightly different string functions

Although JS and Python have sort of converted, with .startsWith and .endsWith etc.

Also related to #950