[Haskell-cafe] Haskell 2020: 'let' to be optional and with wider scope of visibility, like other Haskell functions
Doug McIlroy
doug at cs.dartmouth.edu
Wed Apr 19 20:25:27 UTC 2017
> It's just helping clean up a bit words that doesn't have much meaning.
> Currently GHCi in GHC 8 is supporting this, so you could write both:
>
> x = 10
> x <- return 10
>
> Which is great!
I trust that "x = 10" above does NOT t mean the same as "let x = 10".
If it did, then it wouldn't mean what it does in Haskell.
Then code tried successfully in GHCI could fail in GHC.
Compare this GHCI session
> let x = 10
> :t x
x :: Num a => a
> x + 0.0
10.0
to this, in which x = 10 has its Haskell meaning
> :! cat test.hs
x = 10
> :load test.hs
> :t x
x :: Integer
> x + 0.0
No instance for (Fractional Integer) arising from the literal ‘0.0’.
Doug
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