[Haskell-cafe] Some thoughts on Type-Directed Name Resolution
anthony_clayden at clear.net.nz
Tue Feb 7 03:37:29 CET 2012
Donn Cave <donn <at> avvanta.com> writes:
> You can find stuff like "fromIntegral.ord" in
> packages downloaded to build cabal-install for example. It graphically
> appeals to the notion of a function composed of several functions, so
> the programmers in question will likely not even be repentant!
Data.Char.toUpper -- a name composed of several names
shape.position.xCoord -- a structure composed of several structures
Here's an off-the-wall idea for the syntactics:
- Where there's a block of names with dot separators (and no spaces).
- The dots must be either all postfix apply or all prefix compose.
- Postpone analysing until we've got some type info for the sub-names.
- The types must interlock either left-to-right or right-to-left.
So now we know whether we're prefix or postfix.
- Then we can adjust the AST for loose-binding vs tight-binding.
(As happens for operator precedence.)
?Do we call this "Type-Directed Syntax Resolution" ;-)
(By the way, natural languages do this sort of stuff all the time. In fact
they revel in it:
"Eighth Army Push Bottles Up German Rear."
The more I think about it, the more the pseudo-fields makes sense, the more I
want field selectors to be just functions. There's an interesting example in
Wadler's original paper that became View Patterns "Views: A way for pattern
matching to cohabit with data abstraction" , 4. "Viewing a complex
number in cartesian and polar coordinates".
We may want our implementation of complex to be abstract. We provide (pseudo-)
fields to select the coordinates. Then they're ever-so like methods for an
Also we want the (pseudo-) fields to be updatable, which means field update
needs to be polymorphic (overloaded). Then all I need is a type-(or kind-)
level 'peg' for the name, and an instance for Has/get/set.
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