#14367: Lazy evaluation can be invalidated -------------------------------------+------------------------------------- Reporter: vanto | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: invalid | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by int-e): There is a curiosity here, IMHO: {{{ GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Prelude> :set -fdefer-typed-holes -Wno-typed-holes Prelude> :set -fdefer-out-of-scope-variables -Wno-deferred-out-of-scope- variables Prelude> let x = [_]; y = [r] Prelude> (length x, length y) (1,1) Prelude> length [_] <interactive>:4:9: error: • Found hole: _ :: a0 Where: ‘a0’ is an ambiguous type variable • In the expression: _ In the first argument of ‘length’, namely ‘[_]’ In the expression: length [_] • Relevant bindings include it :: Int (bound at <interactive>:4:1) Prelude> length [r] 1 }}} Why does the `length [_]` expression produce a compile time error? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14367#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler