Slices

[mikeday]

Based on our discussion today about offsets and slices:

Add a binary type for slices that takes a length, the binary type that it should be parsed as, and some optional flags. A slice occupies the same space as [u8; len] but will be parsed as a different binary type. The optional flags can specify whether this binary type must occupy the entire slice or whether there can be trailing bytes left over, and whether links from within the slice can go outside of it. Parsing an entire file can then be considered equivalent to parsing a self-contained slice of the same size.

A label or address type is a zero-length binary type which evaluates to the host value of the current address. An address value can be used as the base address of an offset to create a link.

A link type is a zero-length binary type which takes an address and another binary type to parse at that address. This other binary type can potentially be a slice, so you could have:

offset: u32,
length: u32,
table: link(make_address(base, offset), slice(length, table_type(tag), SelfContained))

Assuming that table_type is a type-level function that maps tag values to binary types, make_address is an expression-level function that combines an address with an integer to make a new address, and SelfContained is a flag indicating that links within this slice cannot go outside it.