Answers

1. Enumeration types are defined with the syntax data ET = K1 | … | Kn, where ET is the name of the type and K1…Kn are the names of the data constructors. Each of the constructors is a value of the enumeration type. Values can be distinguished by means of pattern matching, writing one equation of a function per constructor:

   f K1 = ..
   …
   f Kn = …

2. Record types are defined with the syntax data RT = RK {f1 :: T1, …, fn :: Tn}, where RT is the name of the record type and RK is its constructor. The fields are named f1...fn and have the T1...Tn types, respectively. A value of RT is created with the syntax RT { f1 = e1, …, fn=en}, where e1...en are expressions of the T1...Tn types that yield the values for the fields. Given a value of the record type, a field can be extracted by using the field name as a function, fi :: RT -> Ti.
3. An algebraic datatype is defined with the syntax data AT = K1 T11… | … | Kn Tn1 …...