#10871: Implement "fat" interface files which can be directly compiled without source -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: backpack Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ezyang):
In my (perhaps naive) view of the way this works, "instantiating a unit" is just compiling modules in dependency order, exactly as GHC does today.
No, more has to be done. For example, imagine package foo and bar set up this way: {{{ -- package foo unit foo where signature H module P }}} {{{ -- package bar unit a-impl where module A unit bar where include p include a-impl (A as H) }}} At the end of the day, we need to compile an instance of foo compiled against h-impl, e.g. `foo(H -> h-impl:A)`. How do we know that this is the case? Backpack specifies an ALGORITHM for figuring it out, which involves taking package `bar`, and then doing analysis on the includes (renames and all) to figure out what units are providing modules that other units require. If you support cross-package mutual recursion, this algorithm can be quite tricky indeed, since you need the business with infinite regular trees. So it seems quite desirable for this logic to live in GHC. So no, Cabal cannot just figure out how to instantiate units by looking at the package database, without also implementing a key part of the Backpack algorithms. (In the old design, Cabal DID implement this algorithm, but we really want to get away from that.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10871#comment:24 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler