On 05/08/12 15:55, Phil Clayton wrote:
On 23/07/12 12:51, David Matthews wrote:
What this implies for the implementation is that it needs to actively reduce any type abbreviations to their right hand sides before doing any unification and also when applying the value restriction. This then allows Phil's examples to work and also the simple example above. It does have the unfortunate side-effect that expressions with type abbreviations are not printed using the abbreviation in cases where it used to.
Thanks for the update. I haven't noticed much difference in the printed types. The only change worth mentioning is that
val it = (): unit
now prints as
val it = (): {}
...
I probably spoke a bit too soon here. After more interactive use, it appears that records and tuples can be expanded one level in the types printed back. This can make types much harder to read which may be an issue for those using an interactive session to e.g. inspect expression types by evaluating fragments of code. With the example at the end, 5.4 prints back
val nearest = fn: point -> point list1 -> real * point
which is fairly self-explanatory, whereas r1581 prints back
val nearest = fn: real * real -> (real * real) * (real * real) list -> real * (real * real)
This can be worked around using additional type annotations but that doesn't help for inspecting already written code and some people may not be happy to add so many annotations. (Also, it seems that for function return types, the annotation must go on the rhs.)
Phil
(* Example *)
type 'a list1 = 'a * 'a list fun foldl1 f ((x, xs) : 'a list1) = foldl f x xs fun map1 f ((x, xs) : 'a list1) = (f x, map f xs)
type point = real * real
fun sq (x : real) = x * x
fun distance ((x1, y1) : point) ((x2, y2) : point) = Math.sqrt (sq (y2 - y1) + sq (x2 - x1));
fun nearest p ps1 = let fun nearest2 (i as (di, _), a as (da, _)) = if di < da then i else a fun addDistance q = (distance p q, q) in foldl1 nearest2 (map1 addDistance ps1) end ;