#9256: Support automatic derivation of an hs-boot file from an hs file -------------------------------------+------------------------------------ Reporter: ezyang | Owner: ezyang Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Resolution: | Keywords: backpack Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by goldfire): Thanks. Let me try to spit back what you're saying: {{{ module A where import B data Arf = MkArf (Maybe Bar) }}} {{{ module B where import A data Bar = MkBar (Maybe Arf) }}} The above modules will currently fail to compile because of the import cycle. The current solution is to write an ''A.hs-boot'' file declaring `data Arf` and putting a `{-# SOURCE #-}` pragma in `B`. Your proposed solution is like this: {{{ module A where {-# BOOT_TYPES Arf #-} import B data Arf = MkArf (Maybe Bar) }}} {{{ module B where import {-# SOURCE #-} A data Bar = MkBar (Maybe Arf) }}} Is this correct? I like the idea in general, but there are some pitfalls I see: * An hs-boot file tends to have a mix of `{-# SOURCE #-}` imports and regular imports. The list of imports in the hs-boot file will be different than the list in the master file, and where the `{-# SOURCE #-}` pragma appears will be different. (There's a subset relationship between the import lists, of course.) How will this new syntax figure out which imports are necessary to type check the `BOOT_TYPES`? * It is sometimes desirable to include type ''definitions'' in hi-boot files. How does this syntax accommodate that need? * Similarly, one may want type synonyms and type families available in hi- boot files. How do these work? Thanks! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9256#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler