I have a function map which takes a Parser and a function defined as follows:
def map[T1, T2](parser: Parser[T1], func: T1 => T2): Parser[T2]
I've created a Parser object of type [(Char, Char)] and a function (Char, Char) => String.
val parser[(Char,Char)] = //...
val asString: (Char, Char) => String = (a: Char, b: Char) => a.toString + b.toString
And then I pass these two to the map function.
val mParser: Parser[String] = map(parser, asString)
I expect everything to work fine but I get a type mismatch error for asString argument saying
Error:(26, 41) type mismatch;
found : (Char, Char) => String
required: ((Char, Char)) => String
map[(Char, Char), String](parser, asString)
I have tried to explicitly specify the types for map as map[(Char, Char), String](parser, asString) but that didn't help either.
The type T1 here is the char tuple (Char, Char) and T2 is a String. So, the function (Char, Char) => String is what's supposed to be the input but scala is expecting a different type.
What am I missing here? Why is it expecting ((Char, Char)) => String instead of (Char,Char) => String?
I'm using Scala 2.12. Don't know if that is relevant in any way.
Your help is appreciated.
The type (Char, Char) => String corresponds to a function that takes two Char parameters and returns a String.
What you want is a function that takes a Tuple2 and returns a String which is somehow different.
Its type should be Tuple2[Char, Char] => String.
Tuple2[Char, Char] corresponds to the type shorthand (Char, Char) but I guess during function definition the compiler interprets the parentheses as if they are used to group the function parameters.
This is a known issue and it's being addressed in scala3. https://dotty.epfl.ch/docs/reference/auto-parameter-tupling.html