sub htmlprint {
    my %arg = @_;
    $arg{file}->printf(
      '<span style="color:%s">%s</span>',
      $arg{colour},
      $arg{text},
    );
  }

##</code><code>##

  use Carp qw(croak);
  
  sub htmlprint {
    my %arg = @_;
    exists $arg{file}   or croak "Expected file";
    exists $arg{text}   or croak "Expected text";
    exists $arg{colour} or croak "Expected colour";
    
    $arg{file}->printf(
      '<span style="color:%s">%s</span>',
      $arg{colour},
      $arg{text},
    );
  }

##</code><code>##

  use Carp qw(croak);
  use Scalar::Util qw(blessed);
  
  sub htmlprint {
    my %arg = @_;
    exists $arg{file}   or croak "Expected file";
    exists $arg{text}   or croak "Expected text";
    exists $arg{colour} or croak "Expected colour";
    
    ref($arg{file}) eq 'GLOB'
      or blessed($arg{file}) && $arg{file}->can('printf')
      or croak "File should be a filehandle or object";
    
    defined($arg{text} && !ref($arg{text})
      or croak "Text should be a string";
    
    defined($arg{colour} && !ref($arg{colour})
      or croak "Colour should be a string";
    
    $arg{file}->printf(
      '<span style="color:%s">%s</span>',
      $arg{colour},
      $arg{text},
    );
  }

##</code><code>##

  use feature qw(state);
  use Type::Params qw(compile_named);
  use Types::Standard qw(FileHandle HasMethods Str);
  
  sub htmlprint {
    state $check = compile_named(
      file   => FileHandle | HasMethods['printf'],
      text   => Str,
      colour => Str,
    );
    my $arg = $check->(@_);
    
    $arg->{file}->printf(
      '<span style="color:%s">%s</span>',
      $arg->{colour},
      $arg->{text},
    );
  }

##</code><code>##

  use Type::Params qw(compile_named);
  use Types::Standard qw(FileHandle HasMethods Str);
  
  my $_check_htmlprint;
  sub htmlprint {
    $_check_htmlprint ||= compile_named(
      file   => FileHandle | HasMethods['printf'],
      text   => Str,
      colour => Str,
    );
    my $arg = $_check_htmlprint->(@_);
    
    ...;  # rest of the function goes here
  }

##</code><code>##

  # will throw an exception because of 'size'
  htmlprint( file => $fh, text => "Hello world", colour => "red", size => 7 );

##</code><code>##

  use feature qw(state);
  use Type::Params 1.004000 qw(compile_named);
  use Types::Standard qw(FileHandle HasMethods Str);
  
  sub htmlprint {
    state $check = compile_named(
      file   => FileHandle | HasMethods['printf'],
      text   => Str,
      colour => Str, { default => "black" },
    );
    my $arg = $check->(@_);
    
    ...;  # rest of the function goes here
  }

##</code><code>##

  use feature qw(state);
  use Type::Params 1.004000 qw(compile_named_oo);
  use Types::Standard qw(FileHandle HasMethods Str);
  
  sub htmlprint {
    state $check = compile_named_oo(
      file   => FileHandle | HasMethods['printf'],
      text   => Str,
      colour => Str, { default => "black" },
    );
    my $arg = $check->(@_);
    
    $arg->file->printf(                     # not $arg->{file}
      '<span style="color:%s">%s</span>',
      $arg->colour,                         # not $arg->{colour}
      $arg->text,                           # not $arg->{text}
    );
  }

##</code><code>##

  use feature qw(state);
  use Type::Params 1.004000 qw(compile_named);
  use Types::Standard qw(FileHandle HasMethods Str);
  
  sub htmlprint {
    state $check = compile_named(
      file   => FileHandle | HasMethods['printf'],
      text   => Str,
      colour => Str, { default => "black" },
    );
    my $self = shift;
    my $arg  = $check->(@_);
    
    ...;  # rest of the function goes here
  }

##</code><code>##

  use feature qw(state);
  use Type::Params 1.004000 qw(compile_named);
  use Types::Standard qw(FileHandle HasMethods Str Object);
  
  sub htmlprint {
    state $check = compile_named(
      file   => FileHandle | HasMethods['printf'],
      text   => Str,
      colour => Str, { default => "black" },
    );
    my $self = Object->(shift);  # will die if it's not an object
    my $arg  = $check->(@_);
    
    ...;  # rest of the function goes here
  }

##</code><code>##

  use feature qw(state);
  use Type::Params 1.004000 qw(compile);
  use Types::Standard qw(FileHandle HasMethods Str);
  
  sub htmlprint {
    state $check = compile(
      FileHandle | HasMethods['printf'],
      Str,
      Str, { default => "black" },
    );
    my ($file, $text, $colour) = $check->(@_);
    
    ...;  # rest of the function goes here
  }
  
  htmlprint($fh, "Hello world", "red");
  htmlprint($fh, "Hello world");   # defaults to black

##</code><code>##

  package My::Types {
    use Type::Library -base;
    use Type::Utils -all;
    use Types::Standard ();
    
    declare "FileHandle",
      as Types::Standard::FileHandle;
    
    coerce "FileHandle",
      from Types::Standard::Str, via {
        open(my $fh, "<", $_) or die("Could not open $_: $!");
        return $fh;
      };
  }

##</code><code>##

  use feature qw(state);
  use Type::Params 1.004000 qw(compile_named);
  use Types::Standard qw(HasMethods Str);
  use My::Types qw(FileHandle);
  
  sub htmlprint {
    state $check = compile_named(
      file   => FileHandle | HasMethods['printf'],
      text   => Str,
      colour => Str, { default => "black" },
    );
    my $arg = $check->(@_);
    
    ...;  # rest of the function goes here
  }

##</code><code>##

  htmlprint(
    file => "/tmp/out.html",  # will be coerced to a filehandle
    text => "Hello world",
  );

##</code><code>##

  use feature qw(state);
  use Type::Params 1.004000 qw(compile_named);
  use Types::Standard qw(HasMethods Str);
  use My::Types qw(FileHandle);
  
  sub htmlprint {
    state $check = compile_named(
      file   => FileHandle->no_coercions | HasMethods['printf'],
      text   => Str,
      colour => Str, { default => "black" },
    );
    my $arg = $check->(@_);
    
    ...;  # rest of the function goes here
  }