if then map lookup terraform code example

Example: lookup function in terraform

#lookup retrieves the value of a single element from a map, given its key. 
#If the given key does not exist, a the given default value is returned instead.

lookup(map, key, default)

#Example to Understand

lookup({a="ay", b="bee"}, "a", "what?")
ay

lookup({a="ay", b="bee"}, "c", "what?")
what?