[clean-list] What does the L mean in the expression: : CloudsVertVisibility = L [CloudsVV] | SkyClear

[metaperl]

metaperl wrote:
> 
> I dont understand what the "L" means below. I'm guessing it is a type
> constructor for CludsVertVisibility which takes one argument... Just like
> "SkyClear" is a nullary type constructor.
> 
> 

Yeah, that's clearly what it is. If you look at the instance code you see
pattern matching based on that very same "L" and SkyClear:

instance report CloudsVertVisibility
where	report SkyClear	=  ">05000"
		report (L cs) = case getCeilings cs of
			[]	-> ">05000"
			cs	# visibility = minList cs
				-> " " +++ toDigits visibility 5

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