CS 135 (Module 5: Semantics)

What are identifiers?

They are the names of constants, parameters, and user-defined functions.

What is a syntax?

The way we are allowed to say things.

What are semantics?

The meaning of what we say.

What is ambiguity?

Valid sentences have exactly one meaning.

What do we do to enforce syntax and avoid ambiguity?

We can use grammars.

How do we solve sematics?

We solve it with a semantic model.

What does a semantic model do?

It provides a method of predicting the result of running any program.

How does a sematic model simplify the program?

Via substitution

What are ellipses and what are they used for?

An ellipsis is (...) and it is used to show a patterm. For example: (f v1 ... vn) -> v where v is the value of f(v_1, ..., v_n)

A Racket program is read

top-to-bottom and left-to-right

(cond [false exp] ...) ->

(cond ...)

(cond [true exp] ...) ->

exp

(cond [else exp]) ->

exp

These ellipses are showing an

omission

(and false ...) ->

false

(and true ...) ->

(and ...)

(and) ->

true

(or true ...) ->

true

(or false ...) ->

(or ...)

(or) ->

false

Apply functions only when all arguments are ___

values

When given a choice, evaluate the ____ first

leftmost expression

(f v1...vn) ->

v when f is built-in

(f v1...vn) ->

exp' when (define (f x1...xn) exp) occurs to the left..

id -> val when

(define id val) occurs to the left

What is tracing a program?

Doing a step-by-step reduction according to these rules we have learned.