#14670: -XRebindableSyntax needs return? -------------------------------------+------------------------------------- Reporter: jackkelly | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple RebindableSyntax | Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The documentation for -XRebindableSyntax ( https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts... #rebindable-syntax-and-the-implicit-prelude-import ) reads:
“Do” notation is translated using whatever functions (>>=), (>>), and fail, are in scope (not the Prelude versions). List comprehensions, mdo (The recursive do-notation), and parallel array comprehensions, are unaffected.
The following code fails to compile (also confirmed to fail on GHC 8.0.2): {{{ {-# LANGUAGE RebindableSyntax #-} module Lib where import Prelude (IO) foo :: IO () foo = do pure () }}} It fails with this error: {{{ /home/kel317/z/src/Lib.hs:9:3: error: Not in scope: ‘return’ Perhaps you want to add ‘return’ to the import list in the import of ‘Prelude’ (src/Lib.hs:5:1-19). | 9 | pure () | ^^^^^^^ }}} To my reading, either something funky is going on with the way the do- notation is desugared, or the documentation needs to be corrected. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14670 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler