Is this the sort of thing you are after? It's a PoC as it stands so feel free to tweak until it delivers what you actually want.

use strict;
use warnings;

use Test::More tests => 6;

my $text = 'function convert_wa_date_strings(iv_beg string, iv_end str
+ing, iv_read_date date, iv_step char(6)) returns (date, date, char(1)
+)';

my $re = qr#^(private|public)?\s?(function|report)\s(\w+)\((.+?)\)((?:
+\s+)(returns)\s\((.+)*?\))?$#;


ok ($text =~ $re, 'Matched');
is ($1, undef, '$1 is correct');
is ($2, 'function', '$2 is correct');
is ($3, 'convert_wa_date_strings', '$3 is correct');
is ($4, 'iv_beg string, iv_end string, iv_read_date date, iv_step char
+(6)',
    '$4 is correct');
is ($5, ' returns (date, date, char(1))', '$5 is correct');
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