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Simple snippet that demonstrates recursively defined discriminated unions, the Y combinator (for encoding recursive functions) and recursive processing of tree-like structures
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(* irc.freenode.org, channel ##fsharp <LionMadeOfLions> scientists are baffled, though, it will be decades before we begin to understand the lions made of lions <ninegrid> challenge accepted *) type LionMadeOfLions = Lions | Lion of LionMadeOfLions * LionMadeOfLions let lionMadeOfLions = Lion(Lion(Lion(Lions,Lions),Lions),Lions) (* Lion / \ Lion Lions / \ Lion Lions / \ Lions Lions *) let rec y f x = f (y f) x let understand x = printfn "%A" x let lions (lions : LionMadeOfLions -> LionMadeOfLions) = function | Lion (x,y) -> lions x | Lions -> Lions y (lions >> fun f lion -> understand lion; f lion) lionMadeOfLions (* output: > Lion (Lion (Lion (Lions,Lions),Lions),Lions) Lion (Lion (Lions,Lions),Lions) Lion (Lions,Lions) Lions val it : LionMadeOfLions = Lions *)
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recursion
y-combinator
discriminated unions
recursion
y-combinator
discriminated unions
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