class Opal::Nodes::MatchCurrentLineNode

s(:if, s(:match_current_line, /foo/, true))
$_ = ‘foo’; call if /foo/

def compile

and let :send node to handle it
($_ =~ regexp)
Here we just convert it to 
def compile
  gvar_sexp = s(:gvar, :$_)
  send_node = s(:send, gvar_sexp, :=~, regexp)
  push expr(send_node)
end