Oil Blocks

[andychu]

cd already takes a block:

cd /tmp {
  echo $PWD
}
echo $PWD

Other features it could / will support:

high priority:

• getopts alternative argparse builtin: Replacement / enhancement for getopts #469
• each for xargs

other:

• config files that evaluate to JSON -- need stack name_map -> value.AssocArray
• find alternative (fs or verb walk)
• awk like BEGIN, END, when (wok)
• punted to users: make-like blocks with rule
• much later: lex/yacc dialects with eggex patterns

---

• shopt -- pretty important. Would be nice to refactor errexit first, so we have a stack of flat arrays.

(You could argue if this is "essential", but it carries so much weight that I think it has to be. A lot of it won't make it but some of it should.)

[andychu]

Note, we now have block literals in expression mode like &(echo $PWD)

What else do we need

• shopt needs to take a block (requires refactoring of errexit stack)
• we need some kind of evalexpr() or evalblock() function . User should be able to control the namespace

[andychu]

We need an evaluator with a controlled "first word lookup". Related to #588 first word lookup

User feedback includes use and parse-opts.

• argparse blocks contain flag and arg
• use lib blocks contain use proc

Other:

• They also must turn off globs! Should you just do shopt --set noglob temporarily?
• proc-main for context manager style context manager style for cleanup / trap handlers #861/
• fs . { name '*.py' } is like find . -name '*.py' . So it needs predicates like name and type.
  • it turns OFF errexit
  • maybe it should also turn off globbing so we don't have to quote?

[andychu]

First class blocks don't have a new scope by default:

89bff41

BUT I think evalblock() can push a new temp scope.

[andychu]

Already done:

• shopt
• cd
• fork
• forkwait

Near term list:

• eval
• argparse
• describe?

It doesn't feel like we need blocks for use. #453

Longer term:

• BEGIN, END, when (awk)
• each (xargs)
• fs (find)
• anything like make (rule)

[andychu]

All the eval_block() / eval_to_dict() stuff is now in #951

And builtins are in issues like #863