setOptionFromString
We can use this primitive to process command line arguments of the form `-D <key> = <value>` TODO: allow users to attach `[init]` to definitions of the form ``` @[init] def foo : IO Unit := ... ``` and avoid the awkward auxiliary constant.
Unit.star
Unit.unit
Bool.tt
Bool.true
Bool.ff
Bool.false
function.lean
core.lean
IO.userError
Uint
UInt
Usize
USize