This extension provides syntactic sugar for getting and setting elements
for user-defined indexed types. For instance, we can define python-like
dictionaries with
module Dict = structinclude Hashtbl
let ( .%{} ) tabl index = find tabl index
let ( .%{}<- ) tabl index value = add tabl index value
endlet dict =
let dict = Dict.create 10 inlet () =
dict.Dict.%{"one"} <- 1;
letopen Dict in
dict.%{"two"} <- 2 in
dict
Multi-index are also supported through a second variant of indexing operators
let (.%[;..]) = Bigarray.Genarray.get
let (.%{;..}) = Bigarray.Genarray.get
let (.%(;..)) = Bigarray.Genarray.get
which is called when an index literals contain a semicolon separated list
of expressions with two and more elements:
let sum x y = x.%[1;2;3] + y.%[1;2]
(* is equivalent to *)let sum x y = (.%[;..]) x [|1;2;3|] + (.%[;..]) y [|1;2|]
In particular this multi-index notation makes it possible to uniformly handle
indexing Genarray and other implementations of multidimensional arrays.
module A = Bigarray.Genarray
let (.%{;..}) = A.get
let (.%{;..}<- ) = A.set
let (.%{ }) a k = A.get a [|k|]
let (.%{ }<-) a k x = A.set a [|k|] x
let syntax_compare vec mat t3 t4 =
vec.%{0} = A.get vec [|0|]
&& mat.%{0;0} = A.get mat [|0;0|]
&& t3.%{0;0;0} = A.get t3 [|0;0;0|]
&& t4.%{0;0;0;0} = t4.{0,0,0,0}
Beware that the differentiation between the multi-index and single index
operators is purely syntactic: multi-index operators are restricted to
index expressions that contain one or more semicolons ;. For instance,
let pair vec mat = vec.%{0}, mat.%{0;0}
is equivalent to
let pair vec mat = (.%{ }) vec 0, (.%{;..}) mat [|0;0|]
Notice that in the vec case, we are calling the single index operator, (.%{}), and
not the multi-index variant, (.{;..}).
For this reason, it is expected that most users of multi-index operators will need
to define conjointly a single index variant
let (.%{;..}) = A.get
let (.%{ }) a k = A.get a [|k|]