#13303: Bad pretty printer for let bindings in a do-notation with braces -------------------------------------+------------------------------------- Reporter: rem | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: do-notation, | Operating System: Unknown/Multiple let, parse | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Let bindings in do-notations with braces like this: {{{#!hs module Thing where thing = do {let {x = 1}; print x} }}} get pretty printed with the braces around the bindings stripped, like this: {{{#!hs module Thing where thing = do {let x = 1; print x} }}} Steps to reproduce: copy the module into Try.hs then call: ghc -ddump-rn Try.hs I traced the code to: https://github.com/ghc/ghc/blob/e28fbbb7c3d5904a88b4743d0d10f212d61d8293/com... which points to the pretty printer for list of declarations: https://github.com/ghc/ghc/blob/95dc6dc070deac733d4a4a63a93e606a2e772a67/com... Indeed there is a comment on the two ways to pretty print binders - without braces in multiple lines and with braces in one line. However the comment does not explain the choice, and as discussed in #13302 the former won't parse in a do-notation. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13303 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler