CS61A lect2

Anatomy of a Call Expression：operator, operand
add ( 2 , 3 )

Operator Operand Operand

Operators and operands are also expressions

Evaluation procedure for call expressions:

  1. Evaluate the operator and then the operand subexpressions
  2. Apply the function that is the value of the operator

to the arguments that are the values of the operands

Execution rule for assignment statements:

  1. Evaluate all expressions to the right of = from left to right.
  2. Bind all names to the left of = to those resulting values in the current frame.

Execution procedure for def statements:

  1. Create a function with signature <name>(<formal parameters>)
  2. Set the body of that function to be everything indented after the first line
    1. Bind <name> to that function in the current frame

Procedure for calling/applying user-defined functions (version 1):

  1. Add a local frame, forming a new environment
  2. Bind the function’s formal parameters to its arguments in that frame
  3. Execute the body of the function in that new environment

Most important two things I’ll say all day:

  1. An environment is a sequence of frames.
  2. A name evaluates to the value bound to that name in the earliest frame of the current environment in which that name is found.

Exercise:

What is the value of the final expression in this sequence?

f = min

f = max

g, h = min, max

max = g

max(f(2, g(h(1, 5), 3)), 4)