Lisp Fundamentals

Lisp a malformed acronym for List Processing designed to create computer programs first implemented in the late 1950s by John McCarthy and his associates at MIT has many devotees, especially in the field of artificial intelligence

Why Lisp? great programming environment Used at IRCAM, Grame, CCRMA, CNMAT, MIT, etc. for music

Why programming? Composing and Analysis applications harbor their creator's biases The less bias the more apt you are to get what YOU want.

Why computers? faster more accurate able to tackle large amounts of data NOTE: both paper and computer algorithms

Lisp is: (1) high level (2) functional (3) symbolic (4) interpreted (5) recursive

Programming Credo Divide and Conquer

Programming Credo Divide and Conquer

Programming Credo Divide and Conquer

Programming Credo Divide and Conquer

Programming Credo Divide and Conquer

Lisp Credo Simple is beautiful (kiss) Small is best

Above All Readability everything.

Need a text for reference: A Gentle Guide to Common Lisp By David Touretzky Free online

Need a reference volume: Common Lisp The Language By Guy Steele Free online

Common Lisp Originally available in many flavors, the most used form of Lisp today is Common Lisp, available on every standard computer platform and uniform in use through the standard aforementioned reference manual (Steele 1990).

Assignment #1. Find and download a Common Lisp application (Free ones available for all platforms). Good ones to try: For PCs: Franz Lisp’s Allegro CL Free Express Edition ( For MACs: Clozure CL ( )

Getting started Booting—initializing—Common Lisp typically produces a Listener window ready for command-line input. Typically this produces a prompt such as ?, or >, or :, or whatever, with a blinking cursor to the right, waiting for your input. You’re now ready to begin programming.

How it works input in the Listener window is evaluated—interpreted—by Lisp whenever users follow input with a carriage return

Saving code Code may also be typed into a text window code typed into a text window will not be interpreted until users explicitly invoke it by loading or some other implementation-dependent process (see the Lisp version you use for the documentation)

Information types While many important types of information exist in Common Lisp, the two most important types are functions and data. Functions are operatives that create or alter data in useful ways. Data represent information upon which functions operate.

Functions In Lisp, functions are typically used individually or combined with other functions to produce more complex processes and output. User-defined functions can be included alongside built-in functions, with the results—as the axiom goes—often greater than the sum of their parts.

Data Numbers like etc. Lists ( ) is a list of numbers

Parentheses In order to keep complicated processes in Common Lisp clear, the language requires parentheses, in part to distinguish data and functions, as well as to clarify different functionally initiated actions. In other words, when entering functions or data into a Listener window, users must partition their boundaries and firing order with parentheses.

The single quote all information entered into the Listener window will be evaluated by Lisp unless preceded by a single quote ('). Lisp knows numbers but not lists of numbers. Lisp does not already know letters, words, etc. and these must be preceded by that single quote (').

Example The following code provides a simple example of these concepts, where the "?" represents a typical prompt provided by the form of Common Lisp used: ? (first '(1 2 3)) Produces 1

A closer look: ? (first '(1 2 3)) “First” is a function that Lisp knows (a primitive) that returns the first element of its argument (what follows) ‘(1 2 3) is a list of numbers that Lisp does not know and thus the single quote (‘).

Summary In effect, Common Lisp evaluates the function first with which it is familiar, and then applies that function to the data with which it is not familiar. Functions always appear to the left in a parenthetical representation with data to the right.

A quiz. What will the following produce? ? (1 2)

Error! > Error: Car of (1 2) is not a function name or lambda-expression. > While executing: "Unknown" > Type Command-. to abort. See the Restarts… menu item for further choices.

What will the following produce? ? ‘(first ‘(1 2 3))

Yikes! (FIRST \‘ (1 2 3))

What will the following produce? ? (second ‘(1 2 3))

Yep! 2

You are programming! It’s anal! Don’t expect the program to do anything but what it is designed to do.

How about? (* 1 2) Give it some thought.

Yep! 2 Neither the number 1 nor the number 2 requires single quotes here because Lisp recognizes individual numbers.

Nesting Lisp operations can also be nested to produce more interesting results. ? (first (rest '(1 2 3)))

Produces 2 Lisp first evaluates the function rest (meaning all but the first), which returns the rest of its argument '(2 3), and then evaluates the function first which returns the first element of the result of the rest operation.

Another primitive Lisp provides another primitive—a built- in function that accomplishes very simple things—in this case called second, that produces the same result but using just one function call as in ? (second '(1 2 3)). 2

Sublists Data can also be nested in sublists according to whatever plan the programmer feels will reveal the information best. e.g., (( ) ( ) ( ) ( )...

Lengths Lists can be of any length. This can lead to difficulties in reading or accessing the data. Lisp therefore provides a method of assigning symbols to represent data. By using the Common Lisp function setf allows lots of data to be placed in a single named container.

setf (setf primes ‘( )) allows users to use the symbol primes instead of the numbers themselves. Therefore, once set, placing the symbol primes after the “?” returns the list of primes, since Lisp now understands primes.

As in ? Primes > ‘( )) Now one can use functions to access primes in the same way they can access the actual list as in ? (second primes) 2

More primitives Another Common Lisp primitive, cons, creates lists from—typically—an atom (number or letter) and a list as in ? (cons 1 '(2 3)) returns > (1 2 3)

More than one argument cons requires two arguments, "constructing" (the word from which cons derives) a new list combined from its two arguments.

Other primitives to know length reverse append third to tenth nth (careful) nthcdr (careful) random (careful)

Some more + (can have any number of args) - (can have any number of args) / (can have any number of args) * (can have any number of args) sort (be careful) exp sqrt sin, cosin, tan (etc.)

Predicates Some Lisp functions serve as test functions as in (listp 1) which returns nil because its argument is not a list (atomp ‘(1)) which returns nil because its argument is not an atom The suffix “p” stands for predicate

Conditionals Some functions in Common Lisp— called conditionals—test data for certain attributes. For example, the function if tests its first argument and returns its second argument if it proves true, or its third argument if it proves false.

Example ? (if (numberp 1) t nil) Returns T because “1” is a number and thus the first choice (t) is the result Note that Lisp is case insensitive.

Named This combination is often termed an if- then-else clause.

Quiz ? (if (numberp (second ‘(a 2 b d f)) ‘yes ‘no) returns > yes

Quiz ? (cons 1 (rest ‘( ))) returns > ( ) Whew.

Now you think of some questions!

Remember All Lisp expressions must have matched parentheses; that is, every open paren must appropriately have a closed paren. Document all of your work by placing comments after a “;” or enclosing in “”, or placing between #| this is documentation |# Name variables and everything you do such that later on you can tell what they mean and does.

Remember Readability everything

Let’s try for a few combinations (defvar *my-numbers* ‘(1 2 3)) (if (equal (first *my-numbers*) 2) (third *my-numbers*) (first *my-numbers*)) What’s the answer?

Answer 1

Another (append (append *my-numbers* *my-numbers*) (rest *my-numbers*))

Answer ( )

A little harder (if *my-numbers* (last *my-numbers*) ())

Answer (3) N.B. The function “last” returns a list of the last number. Weird, but true.

Try this: (if (equal *my-numbers* (1 2 3)) (reverse *my-numbers*))

Answer Error! (forget the single quote on data!!!)

Whew! (third ‘((((a)) b)(c ((d) e) f)(((g)) h I))

Answer (((g)) h I))

One flew over the parentheses nest!

Hummmmmmm (+ (first *my-numbers*) (third *my-numbers*) (first *my-numbers*)) Note how much easier the above is to read than: (+ (first *my-numbers*)(third *my- numbers*)(first *my-numbers*)) 4

More exercises (nth 5 ‘( )) 6 Remember to check whether the primitive you’re using is zero or one based as in (nthcdr 5 ‘( )) 6 whew

More? (position 1 '( )) 1 (position 2 '( )) 0 And so on.

From ( ) get: 1) 0 2) 64 3) ) ( ) 5) ( ) 6) ( ) 7) (0 1) 8) ((0)) 9) ( ) 10) (60 0)

From (((a) b) c) get: 1) a 2) c 3) b 4) (a b) 5) (a (b c)))

From (a b c d e) get: 1) (d e) 2) 5 3) (a (b (c (d (e))))) 4) (e d c b a) 5) (a b c d)

From a get: 1) (a) 2) (a. a) 3) (a (a)) 4) ((a) a) 5) (a ())

From a and (b c) get: 1) (a b c) 2) ((a) b c) 3) (a (b c)) 4) (a c) 5) (c b a)

From (a b) and (c d) get: 1) (a b c d) 2) ((a b) c d) 3) ((a b)(c d)) 4) (b a d c) 5) (a (b c) d)

(append '((1)) '(2 3))

((1) 2 3)

(append '((2)(3)) '(4 5))

((2) (3) 4 5)

(first '(((a)) (b c d e)))

((A))

(rest '(((((f))))))

nil

(first '(rest (a b c)))

rest

(first (second '(((1 2))(2 3 4)((5 6 7)))))

2

(second (first '(((1 2))(2 3 4)((5 6 7)))))

nil

Portable Lisp for practice. From now on bring your laptops (with Lisp loaded) to class each time so as we do these you can check them yourself!!!!!

Assignment Aside from bringing your computer and finding and practicing (reading about) lisp, etc. on the website there is a list of questions you will need to answer and turn in next week. We will be getting to music next week, so don’t get nonplussed yet.