use 5.16.1;
use Exporter qw(import);

our @EXPORT=qw{sexpr sexpr2txt};
our @EXPORT_OK=@EXPORT;

sub sexpr
{
        my @stack = ([]);
        local $_ = $_[0];

        while (m{
                \G    # start match right at the end of the previous one
                \s*+  # skip whitespaces
                # now try to match any of possible tokens in THIS order:
                (?<lparen>\() |
                (?<rparen>\)) |
                (?<FLOAT>[0-9]*+\.[0-9]*+) |
                (?<INT>[0-9]++) |
                (?:"(?<STRING>([^\"\\]|\\.)*+)") |
                (?<IDENTIFIER>[^\s()]++)
                # Flags:
                #  g = match the same string repeatedly
                #  m = ^ and $ match at \n
                #  s = dot and \s matches \n
                #  x = allow comments within regex
                }gmsx)
        {
                die "match error" if 0+(keys %+) != 1;

                my $token = (keys %+)[0];
                my $val = $+{$token};

                if ($token eq 'lparen') {
                        my $a = [];
                        push @{$stack[$#stack]}, $a;
                        push @stack, $a;
                } elsif ($token eq 'rparen') {
                        pop @stack;
                } else {
                        push @{$stack[$#stack]}, bless \$val, $token;
                }
        }
        return $stack[0]->[0];
}

sub squote
{ (local $_ = $_[0]) =~ /[\s\"\(\)]/s ? do{s/\"/\\\"/gs; qq{"$_"}} : $_; }

sub sexpr2txt
{
        qq{(@{[ map {
                ref($_) eq '' ? squote($_) :
                ref($_) eq 'STRING' ? squote($$_) :
                ref($_) eq 'ARRAY' ? sexpr2txt($_) : $$_
        } @{$_[0]} ]})}
}

1;