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Newbie Tree Crash Problem
f#

Hello,
I am starting to learn F# while reading Chris Osaki's "Purely Functional Data Structures", doing the exercises in F#, rather than Standard ML. Almost straight away I have a problem ... 

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type Tree = 
	| Node of Tree * 'a * Tree 
	| Empty 

	member this.insert (x: 'a) = 
		match this with 
		| Empty -> Node(Empty, x, Empty) 
		| Node(l, v, r) when x Node(l.insert(x), v, r) 
		| Node(l, v, r) when x > v -> Node(l, v, r.insert(x)) 
		| Node(_) -> this

I try to instantiate the tree with 

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let testTree = Node(Empty, 1, Empty)

and I get an assertion 

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Assertion at reflection.c:10572, condition `i method.count' not met

that eventually brings down the mono runtime. I am awed at my newfound powers of destruction, but can someone point out where I err?

.

Your code is not being displayed properly, so it's hard to know exactly what's wrong. However this code works for me:

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type Tree<'a when 'a : comparison> = 
| Node of Tree<'a> * 'a * Tree<'a> 
| Empty 
  member this.insert (x: 'a) = 
    match this with 
    | Empty -> Node(Empty, x, Empty) 
    | Node(l, v, r) when x < v -> Node(l.insert(x), v, r) 
    | Node(l, v, r) when x > v -> Node(l, v, r.insert(x)) 
    | Node(_) -> this 

let testTree = Node(Empty, 1, Empty)

What environment are you using?

By on 12/30/2010 11:13 AM ()

Thanks for the reply, and thanks for making sense of my careless post. I am using f# 2.0 with MonoDevelop 2.4.1 on mono 2.8.1 on a mac. Your snippet is the same code as I intended to present.

I now find that if I cut and paste the whole sample in my interactive window, the snippet works. If I enter the Tree definition into the interpreter, then put the testTree assignment in separately, it crashes as before.

I haven't tried fsi in a terminal window yet, so I don't know if this behaviour is something to do with Monodevelop or fsharp.

By on 12/30/2010 2:06 PM ()

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