Logic Paradigm - Prolog

• "=": Unify
• "==": Equality
• "is": Evaluate then unify



Example	Meaning	Explanation
x is 3 + 4	x gets 7	is does math, then assigns to the left side
x = 3 + 4	x gets 3 + 4	= assigns to both sides
x == 3 + 4	false, it wasn't already true	== like Java just sees if things are already equal

Logic Paradigm - Prolog

• Provided functions

	returns		returns		returns
integer(3)	true	float(3)	true	string(3)	false
integer(3.14)	false	float(3.14)	true	string(3.14)	false
integer("hi")	false	float("hi")	false	string("hi")	true




	returns		returns		returns
not(true)	false	+(3, 4)	7	string_concat("a", "b")	"ab"
not(false)	true	3 + 4	7
not(integer(3))	false	+(3.1, 4.2)	7.3
not(string(3))	true	3.1 + 4.2	7.3

• Try #1: to add

              foo(A, B):- A + B.
              foo(3, 4). % ERROR undefined procedure (+)/2
            

Cannot find a rule named + which takes 2 parameters. It was expecting a normal rule which returns a boolean.
• Try #2: to add

              foo(A, B, C):- C _____ A + B % =, ==, or is?
            

Which operator to make C be the answer of adding two ints?