2.7. if then else


	Chapter 2. Expressions
2.6. Operators	2.7. `if then else`	2.8. `lambda`

2.7. `if then else`

The expression if E_c then E_t else E_f is a conditional expression. It executes as follows:

If E_c deflates to true, execute E_t.
If E_c deflates to false, execute E_f.
If E_c deflates to a non-Boolean value, halt.
If E_c halts silently, halt.

2.7.1. Syntax

[15] Conditional ::= if Expression then Expression else Expression

2.7.2. Type

The type of if E_c then E_t else E_f is the join of the types of E_t and E_f. Additionally, E_c must have type Boolean.

2.7.3. Examples

− Binary Search in a Sorted Array

{-
  Binary search in a sorted array.
-}

def binary_search(x,a) =
  def searchIn(lo, hi) =
    if (lo >= hi) then 
      false
    else (
      val mid = (lo+hi) / 2
	     val y = a(mid)?
      if (x = y) then 
        true
      else if (x <: y) then
        searchIn(lo, mid) 
      else 
        searchIn(mid+1, hi)
    )
  searchIn(0, a.length?)
      
val a = Array(15)
      
for(0, 15) >i> 
a(i) := 2*i >> 
stop ;

binary_search(19, a) | binary_search(22, a)

{-
OUTPUT:PERMUTABLE
true
false
-}

2.7.4. Related Links

Related Reference Topics