Malcolm Wallace wrote:
Ah, but the reason I want to use field update, rather than a new construction on the rhs, is that my type really has lots of other fields (not mentioned here), which are all of fixed definite types (not parametric). It is much nicer to be able to write
v { field1 = Void }
than
VariantWithOne { field1 = Void , field2 = field2 v , field3 = field3 v , field4 = field4 v , field5 = field5 v ... }
There is no problem with the desirable short version of updating if the type of v does not change! Only for a polymorphic record data type suitable map (or update) functions should be considered. Your long version is (of course) wrongly typed if the type of another field depends on the type of field1. Christian