Entering 0 exprs (whitespace or the empty string) at the REPL gives
an error from `swank:listener-eval`, which subscripts the parse tree
with index 1. (Entering more than one simply ignores all after the
first, assuming that they all parse). We should be a bit more like
R's repl, evaluating each of the exprs in turn and treating the
results a bit like CL's multiple values
Entering 0 exprs (whitespace or the empty string) at the REPL gives
an error from `swank:listener-eval`, which subscripts the parse tree
with index 1. (Entering more than one simply ignores all after the
first, assuming that they all parse). We should be a bit more like
R's repl, evaluating each of the exprs in turn and treating the
results a bit like CL's multiple values