Adapt usage of predefined types in Exercise3

Functional/Exercise/Exercise3.lhs

@@ -106,7 +106,8 @@ We implemented functions `replaceTokenInRow` and `replaceTokenInField`. Reimplem
 
 5) Now that we know about polymorphic structures, let us redefine the `Field` type as follows.
 
-> type Field token = [[token]]
+> -- type Field token = [[token]]
+> type Field token = [] ([] token)
 
 Here, instead of reusing the `Token`s defined in the last exercise, we use a type parameter in order to use the type synonym `Field` with abritrary values.
 Reimplement the function `replaceTokenInField` once more using the predefined higher-order function `map` that works an arbitrary lists; note that for this concrete example, we reuse `Ex.Token`.
@@ -116,12 +117,15 @@ Reimplement the function `replaceTokenInField` once more using the predefined hi
 
 6) We also redefined `CoordMap` using polymorphic lists and pairs.
 
-> type Coord  = (Int,Int)
-> type Coords = [Coord]
+> -- type Coord  = (Int,Int)
+> type Coord = (,) Int Int
+> -- type Coords = [Coord]
+> type Coords = [] Coord
 
 Based on this type synonym we define a type to represent `Coordinate`s as keys and arbitrary tokens as values in order to describe the positions of such tokens. A list of such pairs describes a figure.
 
-> type Figure token = [(Coord, token)]
+> -- type Figure token = [(Coord, token)]
+> type Figure token = [] ((,) Coord token)
 
 Here, we again use a type parameter `token` to use `Figure` with an abitrary type.
 Using this type, we can visualise, for example, the following figure.