scala

Evaluation Order

• From left to right.
• Function arguments evals by value by default.
• You can change this by insert => before type annotation in function defination. For example:

  // instead of
  fn and(a: Boolean, b: Boolean): Boolean =
  	if (a) b else false
  // use eval by name like this
  fn and(a: Boolean, b: => Boolean): Boolean = 
  	if (a) b else false

Function Type

// (Int, Int) => Int
def sum(a: Int, b: Int): Int = a + b
 

Curing

Expansion of Multiple Parameter List

In general, a definition of a function with multiple parameter lists

$$\mathrm{def}f(ar{g}_1)(ar{g}_2)...(ar{g}_n)=E$$

where n > 1, is equivalent to

$$\mathrm{def}f(ar{g}_1)(ar{g}_2)\cdots (ar{g}_{n-1})=\{\mathrm{def}g(ar{g}_n)=E;g\}$$

where $g$ is a fresh identifier. Or for short:

$$\mathrm{def}f(ar{g}_1)(ar{g}_2)\cdots (ar{g}_{n-1})=(ar{g}_n=>E)$$

More Function Types

The type of function bellow is(Int => Int) => (Int, Int) => Int. Note that function types are right associate. So the above type is equivalent to (Int => Int) => ((Int, Int) => Int)

def sum(f: Int => Int)(a: Int, b: Int): Int = ...