CS61A: Lambda Expressions

Lambda Expressions

• Expressions that evaluate to a function.
  • We can directly assign a name to a function without defining it in our frame with def

x = 10
square = x * x              # This expression evaluates to a number
square = lambda x : x * x   # This expression evaluates to a function
square(10)

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• Lambda syntax:
  • lambda <formal parameter> : <return value>
  • “A function with formal parameter that returns the value of return value.”
• The lambda expression is limited to only have a single expression as its return value.
  • Cannot have any additional statements.

Lambda Expressions Versus Def Statements

Lambda	Both	Def
square = lambda x: x * x		def square(x): return x * x
First creates a function with no name, then an assignment statement binds the function to the name	Same parent (frame in which they were defined)	Both binding and function creation happens as a byproduct of def statement (intrinsic naming)

• Hence, the environmental diagrams for lambda functions and def statements are different.
  • Instead of writing a name for the lambda, we denote the function and the frame name as “λ”.
  • However, names can still be bound to the function within a frame.