I think it’s because the “;” is treated as part of the let not part of the do.
After all, how does the implicit layout of the let know that the let-bindings
are finished?
This should work
foo
= do { let { x = 1 };
Just 5 }
Now the let bindings are clearly brought to an end. Or this
foo
= do { let x = 1
; Just 5 }
Now the “’;” is to the left of the x=1 and so brings the let’s implicit layout
to an end.
But not this!
foo
= do { let x = 1; Just 5 }
So it’s a bug in the pretty-printer, not the parser
SImon
From: ghc-devs [mailto:ghc-devs-boun...@haskell.org] On Behalf Of Alan & Kim
Zimmerman
Sent: 10 November 2016 07:01
To: ghc-devs@haskell.org
Subject: ppr of HsDo
The pretty printer turns
foo = do
let x = 1
Just 5
into
foo
= do { let x = 1;
Just 5 }
which does not parse, complaining about "parse error on input ‘Just’"
Is this a parser error or a ppr problem? I am keen to fix the ppr to output
foo
= do let x = 1
Just 5
but I am not sure if there is a parser bug too.
Alan
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