Hi,
Here is a problem -- currently failing -- for type inference in the
interpreter. Consider (taken from current testsuite)
primes == [p := nextPrime(i = 0 => 2; p) for i in 1..]
primes
This currently fails, with roughlty the following diagnostic from
the interpreter
Cannot find a definition or applicable library operation named
nextPrime with argument type(s)
Polynomial Integer
Apparently, the interpreter infers that `p' must stand for a
Polynomial(Integer). I spare you the minutiae of that reasoning, but
basically, it comes to finding a meet for `Integer', for the
expression
i = 0 => 2
and a `Symbol' (promoted to Variable p) for the subexpression `p'
in
i = 0 => 2; p
This seems puzzling, because `we know' that the function `nextPrime'
takes an Integer and produces an Integer. However, the interpreter
does not know that. Rather, the interpreter infers type
`bottom up' fashion, by first computing the type of the operands, and
then use those type to select a function (modemap selection process).
So, the interpreter does not know that `nextPrime' returns an Integer
and use that as a `seed' to the type inferencer.
Looking more at the expression
[p := nextPrime(i = 0 => 2; p) for i in 1..]
is this really something we think is clear cut, unambiguous, and the
interpreter should know how to resolve it?
-- Gaby
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