Learning Functional Data Structures and Algorithms

Argument evaluation

When we call a method (or a function), we could ask for delayed argument evaluation. Following is an example Scala snippet:

scala> def aMethod(x: String) = 
     |   println(x) 
aMethod: (x: String)Unit 
 
scala> aMethod("Hello world") // call site 
Hello world  

The method argument is evaluated at the call site. However, recall that functions are first class values. This allows us to write the method as follows:

scala> def aMethod_1(x: () => String) = 
     |   println(x()) // argument evaluated 
aMethod_1: (x: () => String)Unit 
 
scala> aMethod_1(() => "Hello world") // unevaluated argument  
Hello world 

When aMethod_1 is called, the string argument is not evaluated at the call site. Inside the method definition, the function is called and the argument ...