[Haskell-cafe] Very binding semicolon

[Branimir Maksimovic]

Why this works :P
bmaxa at Branimirs-Air haskell % ghc -O2 semi.hs
Loaded package environment from /Users/bmaxa/.ghc/aarch64-darwin-8.10.7/environments/default
[1 of 1] Compiling Main             ( semi.hs, semi.o )
Linking semi ...
bmaxa at Branimirs-Air haskell % ./semi
[1,2,3,3,2,1]
bmaxa at Branimirs-Air haskell % cat semi.hs
main = do
  let lst = lrl [1,2,3]
  print lst
; ; ; ; ; ; ; ;;;;lrl :: [a]->[a]; ;; ; ; ; ; lrl xs = xs ++ reverse xs

> On 28.09.2021., at 12:00, Anthony Clayden <anthony.d.clayden at gmail.com> wrote:
> 
> From the department of improbable syntax/I don't get how this works, but it does:
> 
> >    f :: [a] -> [a]
> >    ;; f xs = xs ++ reverse xs
> 
> Nicely (to my eye) groups/indents the binding under the signature. Especially handy with ScopedTypeVariables, to show how the scoped vars 'belong'
> 
> >    f       :: forall a. [a] -> [a]
> >    ;; f xs = xs ++ ys
> >       where
> >         ys :: [a]
> >         ys = reverse xs
> 
> The doubled `;;` stands out like a ditto. It could be a single semicolon (which means there's an empty decl/binding between the semis -- I don't see that's allowed by the syntax).
> 
> Unfortunately, for multi-line bindings you need to repeat the `;;`
> 
> >    f       :: [a] -> [a]
> >    ;; f [] = []
> >    ;; f xs = xs ++ reverse xs
> 
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