#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

{   package My;
    sub new { bless {}, shift }
}

use Function::Parameters;
use Types::Standard qw( InstanceOf );

fun validate(InstanceOf['My'] $m) {  # <- Fails :-(
    say "object:", $m;
}

my $m = 'My'->new;
validate($m);

##</code><code>##

In fun validate: missing type name after '[' at 1.pl line 13.

##</code><code>##

fun validate((InstanceOf['My']) $m) {  # <- Works :-)
#            ~                ~