On Feb 13, 2014, at 2:51 PM, Sam Tobin-Hochstadt wrote: >> (for/sum: : Flonum [[ii : Index 300]] >> pi) >> >> and I get the type error "Expected Flonum, but got Zero". Where is there a >> zero anywhere in this code? And even if there were a zero, shouldn't Zero >> be a subtype of Flonum? >> >> Don't tell me the Zero I'm running into is the initial value of for/sum's >> hidden accumulator.... > > Unfortunately, that's exactly what I'm going to tell you. Typed > Racket isn't smart enough to know that the initial value is never > used, and so 0 is thought to be a possibility.
Doesn't that make for/sum: useless for anything other than exact integers? Couldn't for/sum: initialize its accumulator to a Real-Zero rather than the overly-specified type Zero? (That would rule out complexes, but it would be a big step in the right direction.) (Should there be a Complex-Zero type?) Even better, could for/sum: look at the annotation type and decide what initial value (0 or #i0.0) to use? > I recommend using `for/fold` for this case as a workaround. OK, I'll try that. Stephen Bloch sbl...@adelphi.edu GPG key at http://adelphi.edu/sbloch/sbloch.pubkey.asc
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