Highlights of chapter 2, Winston and Horn

Lisp procedures and data are symbolic expressions

1. (+ 3.14 2.71)

This is a list with 3 elements separated by spaces.

The procedure (or function) is always specified first, followed by the arguments (parameters).

3.14 and 2.71 are the parameters to the function ‘+’.

This is called prefix notation.

We’re using procedure and function synonymously.
  1. + is a primitive - a procedure supplied by Lisp itself

    2. A user defined procedure is supplied (defined) by the programmer.

    A collection of procedures that work together is called a program.

    An algorithm is a specification for how to do something.

    An algorithm is a abstract specification that must be concrete enough to be recast as a procedure.

  2. Atoms are indivisible things like 27, 3.14, +, FOO B27, and HYPHENATED-SYMBOL

    3. Numeric atoms (numbers): 27 and 3.14

    Symbolic atoms (symbols): FOO B27, HYPHENATED-SYMBOL, FIRST, and +

  3. Lists consist of a left parenthesis, followed by zero or more atoms or lists, followed by a right parenthesis.
  4. Symbolic expressions: both atoms and lists are called symbolic expressions (or expressions)

Chapter summary

Lisp means symbol manipulation. Lisp stands for List Processing.

Lisp procedures and data are symbolic expressions.

FIRST and REST take lists apart. (also SECOND, THIRD, etc.)

CAR and CDR are older versions. (also CADR, CADDR, etc.)

Quoting stops evaluation.

SETF assigns values to symbols.

SETF accepts multiple symbol-value pairs.

Certain atoms evaluate to themselves. (T, NIL, and numbers)

CONS, APPEND, and LIST construct lists

CONS, APPEND, and LIST do not alter symbol values

NTHCDR, BUTLAST, and LAST shorten lists. Each of these returns a list.

LENGTH and REVERSE work on top-level elements.

ASSOC looks for indexed sublists.

(setf sarah ‘((height 0.54) (weight 4.4)))

(assoc ‘weight sarah) returns (WEIGHT 4.4)

Lisp offers integers, ratios, and floating point numbers

(/ 22 7) returns 22/7, (float (/ 22 7)) returns 3.14285…

A few primitives make up a basic repertoire: MAX, MIN, EXPT, SQRT, ABS