One small point of terminology, "param" _never_ returns an array. It returns a list. The difference can be important.

Here's some code that does what (I think) you want.

my %params;

foreach (param) {
  $params{$_} = [ param($_) ];
  $params{$_} = $params{$_}[0] if @{$params{$_}} == 1;
}
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You'll end up with a hash (%params) that contains a key/value pair for each parameter name. If the parameter is single-valued the value will contain that (single) value. If the parameter is multi-valued, then the value will be a reference to an anonymous array containing all of the values.