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Tail recursion modulo cons




<programming, compiler> A generalisation of tail recursion introduced by D.H.D. Warren.

It applies when the last thing a function does is to apply a constructor functions (e.g. cons) to an application of a non-primitive function.

This is transformed into a tail call to the function which is also passed a pointer to where its result should be written.

E.g.

f []



= [] f (x:xs) = 1 : f xs

is transformed into (pseudo C/Haskell):

f [] = [] f l

= f' l allocate_cons

f' []



p = *p = nil; return *p f' (x:xs) p = cell = allocate_cons; *p = cell; cell.head = 1; return f' xs &cell.tail

where allocate_cons returns the address of a new cons cell, *p is the location pointed to by p and &c is the address of c.

[D.H.D. Warren, DAI Research Report 141, University of Edinburgh 1980].



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