I am new to haskell. Somebody gave me a symbol and a formula: m & n = n m But "&" can't be read by ghci,and we searched the Internet and found no information. Could anyone tell me what the & means?
2 Answers
It's an identifier without any special meaning, so it means whatever you want it to. E.g. in Lens & is used as flip ($) for convenience, like so:
let x = (1,2)
& _1 +~ 1
& _2 +~ 2
-- x = (2,4)
This also fits your definition of m & n = n m (they're equivalent). Any other library can use it for whatever, and if you use a better search engine, you'll find numerous ones.
(&) operator is defined in Data.Function package. To use it in ghci you have to import Data.Function
Then you can use it with the meaning given by the formula you posted.
> pi & cos
-1.0
Same as:
> cos pi
-1.0
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