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REDUCERON MEMO 11 (ABANDONED)
Enabling arity-raising by sharing analysis
Matthew N, 3 December 2008
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Suppose that for every function 'f' in a program we introduce a
function 'f*', the arity-raised version of 'f'.

What we'd like to do is to go through a program and replace calls to
'f' with calls to 'f*'.  Under what circumstances can we do this,
without losing sharing?

  Any application of 'f' being passed as an argument to a function that
  is linear in that argument can be replaced with an application of
  'f*'.

What does it mean for a function to be linear in an argument?

The body of a function 'f' is linear in argument 'v' if 

  it is any expression containing 0 references to 'v'

  OR

  it is an application of a function 'g' of arity 'n' to 'm' arguments
  AND one of the first 'min n m' arguments contains one reference to 'v'
  AND that argument is linear in 'v'
  AND the body of 'g' is linear in the variable at that argument position
  AND none of the final 'nat(m-n)' arguments contains a reference to 'v'

  OR

  it is a case expression
  AND the subject does not contain a reference to 'v'
  AND each alternative is linear in 'v'

  OR

  it is a case expression
  AND the subject does contain a reference to 'v'
  AND the subject is linear in 'v'
  AND each alternative does not contain a reference to 'v'
  AND each alternative is linear in its each of its pattern-bound variables

  OR

  it is a let expression
  AND the body references 'v'
  AND the body is linear in 'v'
  AND no binding references 'v'

  OR

  it is a let expression
  AND the body does not reference 'v'
  AND one binding binds a variable 'w' to an expression referencing 'v'
  AND that expression is linear in 'v'
  AND the let expression is linear in 'w'

  OR

  it is a variable

(ABANDONED)