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I'd appreciate if someone could point to docs on what "let" does in GHCi, or failing that, explain it convincingly.
So far as I can tell, "let" (without "in") is not part of the Haskell language per se, and on the other hand, it doesn't appear to be a GHCi command either, as it's not prefixed by colon.
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Let bindings let you bind to variables anywhere and are expressions themselves, but are very local, so they don't span across guards. Just like any construct in Haskell that is used to bind values to names, let bindings can be used for pattern matching.
Simply type a let followed by a newline: let ⏎. Then fac 0 = 1 ⏎. Then fac n = n * fac (n-1) ⏎ ⏎ and you're done!
Quits GHCi. You can also quit by typing control-D at the prompt. Attempts to reload the current target set (see :load ) if any of the modules in the set, or any dependent module, has changed.
GHCi is the interactive interface to GHC. From the command line, enter "ghci" (or "ghci -W") followed by an optional filename to load. Note: We recommend using "ghci -W", which tells GHC to output useful warning messages in more situations. These warnings help to avoid common programming errors.
While programming in GHCi, you're like programming in the IO monad with do syntax, so for example you can directly execute an IO action, or use monadic bind syntax like r <- someIOFun.
let is also a part of do so you can also use this. I think it's being desugared into let .. in <rest of the computation>, so for example when you do this:
ghci> let a = 1 ghci> someFun ghci> someFun2 It's like:
let a = 1 in do someFun someFun2 If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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