Introduction to Computational Linguistics

9. Objects and Methods 23
of type ’a to objects of ’b -> ’a. It is legitimate to apply it to just one object:
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# k "cat";;
− :
’_a −> string =
This means that if you give it another argument, the result is a string (because the
result is "cat"). You can check this by assigning an identifier to the function and
applying it:
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# let katz = k "cat";;
val katz : ’_a −> string =
# katz "mouse";;
- : string = "cat"
Effectively, this means that you define functions by abstraction; in fact, this is
the way in which they are defined. However, the way in which you present the
arguments may be important. (However, you can define the order of the arguments
in any way you want. Once you have made a choice, you must strictly obey that
order, though.)
9 Objects and Methods
The role of variables is played in OCaMl by objects. Objects are abstract data
structures, they can be passed around and manipulated. However, it is important
that OCaML has to be told every detail about an object, including how it is accessed,
how it can communicate the identity of that object to you and how it can
manipulate objects. Here is a program that defines a natural number:
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class number =
object
val mutable x = 0
method get = x
method succ = x