[mercury-users] mode/inst etc

[Tomas By]

Hello,

Suppose I have a type:

  :- type tree(K,V) ---> empty ; tree(K,V,tree(K,V),tree(K,V)).

and a procedure that is only ever called for a non-empty tree:

  :- pred dosomething(tree(K,V)::in,K::out,V::out) is det.

I could write

  dosomething(tree(K,V,_,_),K,V).
  dosomething(empty,_,_) :- error("Tree is empty").

but it would be nicer if I could tell the compiler to not allow the tree
to be empty. Perhaps something like

  :- mode intree == in(tree(bound,bound)).

  :- pred dosomething(tree(K,V)::intree,K::out,V::out) is det.

Is this possible? What should the code like? (The above does not work)

/Tomas



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