David Snider wrote:
OK, Thanks. There are some other things I don't understand:
"With sum defined, it is easy to make some sample calls. The form of the
code for main does not make it apparent, but the compiler must "reverse
engineer" the appropriate {Unit} from the {Type} available from the context
at each call to sum. The compiler also infers a folder for each call,
guessing at the desired permutations by examining the orders in which field
names are written in the code."
I understand type inference, but how does it infer the actual values of the
parameters? How do I know which parameters need to be passed and which will
be inferred?
I believe this is addressed in the manual:
http://www.impredicative.com/ur/manual.pdf
See Section 4.3, in a paragraph beginning "Handling of implicit...".
This comes near the top of page 14 in the current manual. It might also
help to look at the "Explicitness" non-terminal "?", defined at the
bottom of page 9 and used in a few places in the next few pages.
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