Design for Python-like functions in Oil

[andychu]

This issue was mentioned here

http://www.oilshell.org/blog/2021/12/review-arch.html

And many related issues

• allow users to write obscure shell operators with function call syntax #616
• Oil language should distinguish between variables and functions/queries ($PWD vs. pwd, etc.) #787
• uniform function call syntax #950
• not sure: Implement proper functions and get rid of setref? #968
• Protocol for defining small functions in external binaries #1026
• Implement builtin sub (fast command sub) #1275

https://oilshell.zulipchat.com/#narrow/stream/121540-oil-discuss/topic/Python-like.20functions.20.28errexit.20issue.20and.20docs.29

[andychu]

It's related to error handling, because procs have exit codes, and a expression like 1 / 0 logically raises an exception

• test and document var x = $(false) #942

[andychu]

Key question: Are functions vectorized ?

I think they can use QTT for args and return values. So you get the args on stdin. And then you return on stdout.

And a non-zero exit code is turned into a fatal "exception"? It aborts the recursive expression evaluation, which again turns into an exit code at the statement/command level.

Something like this, but we also need headers

proc myfunc {
  while read --qtt :left :right {
    write -- $[left + right]
  }
}

Or maybe

proc myfunc {
  read-qtt-header  # suppose the header is "left right".  Maybe it fills _schema or _header
  while read-qtt-row {
    write $[_row->left + _row->right]
  }
}

define :myfunc {  # this is a builtin that assigns to a variable?  functions are variables that wrap procs?
  format = 'qtt'  # can also be JSON for non-primitive data
}

Do we have multiple types of functions -- vectorized and non-vectorized?

The vectorized ones are more typed with QTT ?

[andychu]

I think we should consider putting user-defined functions and builtin functions in the "proc" namespace, sort of like a Lisp 2

And then have var len = get_func('len') and var foo = get_proc('foo') to unify them. I guess you might need that for sorting comparators or something?

$ bin/osh -c 'echo $len'
  echo $len
  ^~~~
[ -c flag ]:1: fatal: Expected evaluation to Bool, Int, or Str.  Got <type 'builtin_function_or_method'>

[andychu]

Feedback here on potential (syntactic and semantic) confusion between procs and funcs

https://oilshell.zulipchat.com/#narrow/stream/264891-oil-help/topic/_.20versus.20.28.29.20for.20append

It is a hard design problem

[andychu]

Done - future work described here https://www.oilshell.org/blog/2024/01/release-0.19.0.html