#14527: Warn on recursive bindings -------------------------------------+------------------------------------- Reporter: chrisdone | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: 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 nh2): **GHC 7.10 already had this feature**, but it disappeared with 8.0, and it's not clear to me if intentionally or accidentally. It would be great to find out. In 7.10, you could simply used a BangPattern to forbid recursive variable bindings. Example {{{ Recursive bang-pattern or unboxed-tuple bindings aren't allowed: !x = x }}} And it said in the manual: {{{ a bang-pattern binding must be non-recursive }}} It was removed for GHC 8.0 in these commits: * https://github.com/ghc/ghc/commit/e7985ed23ddc68b6a2e4af753578dc1d9e8ab4c9 #diff-47b9f40b0ede605e7b6bcb330b43ad53L1678 * https://github.com/ghc/ghc/commit/46a03fbec#diff- 02e7842997523ff8a5ad0312df2edfe2L10348 The question is: Why was this removed? Was it accidental, or did people find a legitimate use case for strict recursive variable let bindings? If not, we could simply re-introduce that, without a language extension (though we might still add the proposed language extension to get warnings even without bangs). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14527#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler