(** [match_value p v] matches the value [v] against the pattern [p]
and returns all bindings caused by the matching, in the order
of their appearances in the pattern [p]. If the value does not
match the pattern, it returns [None].
A helpful idea is to think of it as [let p = v] in OCaml.
What new bindings should be introduced after running
[let p = v]. If bindings are created, the function should
return the bindings as an association list. Otherwise,
if the pattern matching fails, the function should return
[None]. The semantics should agree with OCaml. This homework
requires you to reflect upon what you have learned and
codify your knowledge into programs.
For example, [match_value (PVar “x”) (VNum 100)] will return
the value [Some [(“x”, VNum 100)]] because the variable pattern
[x] matches any value. The corresponding OCaml code is
let x = 100
After this line, the variable [x] is bound to [100]. The code
thus should compute the mapping [(“x”, VNum 100)]].
Another example is [let (x, y) = (42, ())], which should create
two bindings: [x] is mapped to [42] and [y] is mapped to [()].
In our representation, this means
match_value
(PTuple [PVar “x”; PVar “y”]) (* The pattern [(x, y)] *)
(VTuple [VNum 42; VTuple []]) (* The value [(42, ())] *)
should return [Some [(“x”, VNum 42); (“y”, VTuple [])]].
The binding [x] is before [y] because [x] appears first.
Yet another example is [match_value (PNum 10) (VNum 10)],
which should return [Some []] because the numbers match but
the pattern creates zero bindings.
On the other hand, [match_value PTrue VFalse] should return
[None] because [true] does not match [false]. *)
val match_value : Syntax.pattern -> Syntax.value -> (string * Syntax.value) list option