I left out a combinator:
BEXPR_aprj (expr, d,c)
This is an array projection. The BEXPR_prj (n,d,c) requires a constant n,
so is only useful for tuples, records, and structs.
The expression expr has to be a type which can index an array.
The most basic (and probably only) such type is:
BEXPR_case (i,n)
i.e. a unit sum of n units (type "n") aka
i modulo n
where the array bound is n. However if an array has a compact linear index type
t,
then it can be accessed by a subscript of type t. For example a matrix
T ^ 2 ^ 3
is an array of 3 pairs of T, which requires two projections. However it's
isomorphic to
T ^ (3 * 2)
so could be indexed by a tuple of type 3 * 2. Of course that tuple is compact
linear
and so the index can be converted to type 6. In any case the index which is a
tuple
could look like
BEXPR_tuple [BEXPR_case (1,3); BEXPR_case (1,2)] // (1,1)
--
john skaller
[email protected]
http://felix-lang.org
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