#10796: Illegal data constructor name: `fromList' ... When splicing a TH expression -------------------------------------+------------------------------------- Reporter: erisco | Owner: RyanGlScott Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Template Haskell | Version: 7.8.3 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1313 -------------------------------------+------------------------------------- Comment (by RyanGlScott): On the discussion for Phab:D1313, Richard noted that in order to fix this bug properly, it would be necessary for `template-haskell` to know precisely which identifiers correspond to variables, and which correspond to data constructors. This can be surprisingly tricky, since a litmus test for variables vs. constructors must take into account infix symbols and special characters (e.g., [https://ghc.haskell.org/trac/ghc/ticket/1103 Japanese katakana or hiragana]). Such a task seems best left to a function separate from `dataToQa`, but which one? There's [https://git.haskell.org/ghc.git/blob/ea4df12f7f3fc4d1d2af335804b8ec893f45550... startsVarSym, startsVarId, startsConSym, and startsConId] from `Lexeme` in GHC, but `template-haskell` can't depend on GHC. We ought not move these to `base` either, since that we need this functionality to compile stage 1. Therefore, it seems apt to move this to a package which both `ghc` and `template-haskell` could depend on. Luckily, there's some momentum behind this already: Simon PJ [https://phabricator.haskell.org/D1200#33621 suggested] reappropriating the `bin-package-db` package to become a library which contains functionality that is needed across multiple GHC boot libraries (including GHC itself). Less fortunately, we'd probably need to give it a new name to reflect this. Here is what I propose to resolve this quagmire: 1. Rename `bin-package-db` to `ghc-common` (other naming suggestions are welcome). 2. Move `startsVarSym`, `startsVarId`, `startsConSym`, `startsConId`, `startsVarSymASCII`, and `isVarSymChar` from `Lexeme` to `ghc-common`. There are other things that could be moved, but these would be enough to fix this ticket, and don't rely on a GHC internal data type (e.g., `FastString`). 3. Make `ghc` and `template-haskell` depend on `ghc-common`. No other changes to `ghc` should be necessary. 4. Use `startsVarSym` and `startsVarId` to check if a string corresponds to a variable name within `template-haskell`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10796#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler