_n(b: binding): text

If _length(b) == 1, returns the name part of the <name, value> pair that constitutes b. Otherwise, returns ERR.

_n([foo = 1]) == "foo"
_n([ bar = TRUE, msg = "a string" ]) == ERR            // Binding is not length 1
_n(_head([ bar = TRUE, msg = "a string" ])) == "bar"

_v(b: binding): any

If _length(b) isn't 1, returns ERR. Otherwise, this function returns the value part of the <name, value> pair that constitutes b. (Note that a result value of ERR does not imply that _length(b) differs from 1, since the value may be ERR.)

_v([foo = 1]) == 1
_v([ bar = TRUE, msg = "a string" ]) == ERR            // Binding is not length 1
_v(_head([ bar = TRUE, msg = "a string" ])) == TRUE