function definitions in haskell interactive

Question

factorial :: Integer -> Integer
factorial n = product [1..n]

The following is fine:

let factorial n = product [1..n]

I do not see how to add type declarations in interactive shell.

Why do you want to add type declarations? Haskell will always attach the most generic signature to the function. In this case: `(Enum a, Num a) => a -> a` — Willem Van Onsem, Sep 15 '15 at 14:05
possible duplicate of [How to provide explicit type declarations for functions when using GHCi?](http://stackoverflow.com/questions/3093133/how-to-provide-explicit-type-declarations-for-functions-when-using-ghci) — Sam van Herwaarden, Sep 15 '15 at 14:23

Sam van Herwaarden · Accepted Answer · 2015-09-15T14:59:02.597

5

If you want to specify the type signature yourself you can do this in ghci using semicolons, i.e.:

let factorial :: Integer -> Integer; factorial n = product [1..n]

edited Sep 15 '15 at 14:59

answered Sep 15 '15 at 14:17

2

To be super picky, the reason this works is that it is one statement, a let statement containing two declarations. It parses as `let { factorial :: Integer -> Integer; factorial n = product [1..n] }`. – Reid Barton Sep 15 '15 at 14:58

score 5 · Answer 2 · edited May 23 '17 at 12:14

5

Next to the multi-line settings explained here, you can use this instead if you don't want to write semicolons.

λ> :{
λ> | let factorial :: Integer -> Integer
λ> |     factorial n = product [1..n]
λ> :}
λ> :t factorial
factorial :: Integer -> Integer

edited May 23 '17 at 12:14

Community

answered Sep 15 '15 at 14:43

Cirquit

Tip: You can put a newline after the `let` and then don't need to indent the rest. – Ørjan Johansen Sep 15 '15 at 22:45

2 Answers2