Support parameterised hash table type declarations

[evhan]

As suggested by megane on ​chicken-hackers.

Support specifying the types of hash table keys and values:

(define t (the (hash-table fixnum symbol) ...))

(hash-table-ref t 'foo) ; warning "expected argument #2 of type `fixnum' but was given an argument of type `symbol'"

(hash-table-ref t 42) ; result would be known to be a symbol

And so on.

[megane]

Btw, I was not targeting specifically hash-tables, but general user defined types.

Here's an alternative patch.

This codes the parameters into a list in the third element,
(struct name (param ...)).

Some features of the matcher:

• (struct foo #f) == (struct foo)

• (struct foo (* ...)) is simplified into (struct foo)

• (struct foo #f) matches with (struct foo any-list)

• If A and B are lists, then (struct foo A) and (struct foo B) only match if (= (length A) (length B)) and all the elements of A and B match.

For example, giving (struct foo (a)) where (struct foo (* b)) is
expected causes a type warning.

[megane]

Here's another prototype.

These stay same:

• (struct foo #f) == (struct foo)
• (struct foo #f) matches with (struct foo any-list)
• If A and B are lists, then (struct foo A) and (struct foo B) only match if (= (length A) (length B)) and all the elements of A and B match.

New things

• does not simplify (struct foo (* * ...))
• smashes (struct foo (A B ...)) into (struct foo (* * ...))

I think hash-table-set! cannot be #:clean. For example vector-set! is not. So you cannot get key/value related type warnings from setters, unless -strict-types is used.