CS 5541 (AI): A Few Quick Thoughts on Emacs, LispRunning emacsSome Useful emacs CommandsIlisp menu optionsBasics of LispLisp ListLisp List (cont)Running LispPrograms in LispSimple ProgramFunction Definition (named)Some Basic FunctionsList ManipulationMultiple Command StructuresControl StructuresLoop Structure – Do Other LoopsAnother Data Structure - ArraysInput/OutputUseful MacrosCS 5541 (AI): A Few Quick Thoughts on Emacs, LispRich MaclinComputer Science DepartmentUniversity of Minnesota DuluthRunning emacs• To run, simply type emacs on the command line of an xterm• To run clisp in the ilisp p ackage type Alt‐X run‐ilisp, then when prompted to clisp, this will break your windows into two windows (one an editor and one the lisp interpreter)• You can find many lists of emacs commands online, this is a reasonable one: http://www.physics.ohio‐state.edu/~driver/Emacs_Quick_Reference.pdfSome Useful emacs CommandsMost can be done with emacs menu• C‐x C‐f –open or create file• C‐x C‐s –save file• C‐x s –save all buffers• C‐x C‐w –write file• C‐x C‐c –exit emacs• C‐g –cancel current command• C‐x C‐b – list all buffers• C‐x b name –shift to named buffer• C‐x k – kill bufferIlisp menu optionsLook for ilisp on menu• Load file –load generally a definitions file• Eval region – evaluate highlighted region in buffer in lisp• Eval defun – evaluate the surrounding defunstatement in the buffer• Lots of other useful commandsBasics of Lisp• Basic data types– Numbers– Symbols ‘A is the symbol A– Character is #\X –character X– #( … ) is a vector– “ … “ is a string– nil is the null list ‐ as is ‘()– True is anything not nil (can use t) – Lists can be lists of any type of object (can mix things together)Lisp List• A list consists of cons cell(s):• A cons has a first and a rest part of it. Mostly lists of items consists of one cons per item with a pointer to the null list at the end• ‘(1 A “string”) is ‘(1 . 2) is1A“string”nil1 2Lisp List (cont)• ‘ before ( or symbol is equally shorthand for (quote …) command, ‘A is the symbol A• Can also construct list as (list 1 A “string”)• Can have arbitrary lists within lists‘(1 (2 A) (3 (“string”) 4) 5)Running Lisp• Lisp is generally run as an interpreter (though it can be compiled)• A Lisp program is generally a file or files defining a set of functions (plus macros, global parameters, etc.)• The file(s) are loaded into the interpreter and generally called from the command linePrograms in Lisp• Programs in lisp are written as sets of interacting functions• Often the program is run by typing a function call at the command line• The basic syntax of Lisp is( functionName arg1 arg2 arg3 … )• You can call Lisp functions or write your ownSimple Program(defun factorial (x)(if (<= x 0)1(* x (factorial (- x 1)))))Type in to define then try calling (factorial 5)Function Definition (named)(defun functionName ( arguments )body)Name is any reasonable nameArguments are named pass by value argumentsThe body (should) be a single function call where the value of that call is returned as the value of the function, in practice Lisp lets you list multiple function calls in the body and then the value of the function is the last oneSome Basic Functions(+ number number …)Also ‐, *, /(< number number )Also >, <=, >=, ==, (and value value …)Also or(not value)(eq value1 value2)Also eql, equal, equalp(null item)Assignment:> (setq a 5)…> A5setf a more powerful version (macro that works on some function calls)List Manipulat ion(setq a ‘(1 (2 3) 4 5 (6)))(car a) is 1(cdr a) is ((2 3) 4 5 (6))(cadr a) is (2 3)(caadr a) is 2(cdadr a) is (3)(cddr a) is (4 5 (6))(caddr a) is 4(cdddr a) is (5 (6))(nth 0 a) is 1(nth 3 a) is 5(nthcdr 3 a) is (5 (6))first is equivalent to carrest is equivalent to cdr(cons a b) creates a cons cell of a b(list items) creates a list of the items items(append lists) glues lists togetherMultiple Command StructuresTemporary variable declaration (series of variable names, values in lists)(let((x 5)(y 6))body of let)let* evaluates arguments in order (can use earlier temporary variable names in lat er variable values)Evaluate set of commands(progn commands) –evaluate commands in order, return value of last(prog1 commands) –evaluate commands in order, return value of firstSome dialects have other commands (e.g ., prog2)Control Structures(if expr truestmt falsestmt) –if expr is true evals truestmt, otherwise evals falsestmt(when expr form1 form2 …) –if expr is true evals form1, etc. in order(unless expr form1 form2 …) –if expr is false evals form1, etc. in order(cond(expr1 form11 form12 form13 …)(expr2 form21 form22 form23 …)(expr3 form31 form32 form33 …)..) –evaluates expr1, if true evaluates form11, form12, et c. in order, if expr1 is false evaluates expr2 and if true evaluates form21, form22, etc. in order, in all cases returns the value of the last form evaluatedLoop Structure –Do (do((var1 val1 nextval1)(var2 val2 nextval2)…)(endtest result)commandlist)(do((i 0 (+ i1))(x nil))((null (nthcdr i lst)) x)(push (nth ilst) x))do* is the same except the variable list is declared sequentiallyOther Loops(dolist (varname list) commands) –set the variable name varname to each of the items in list in turn and evals commands(dotimes (varname integerarg result) commands) –set the variable name varnameto each value from 1 to integerarg‐1 evalscommandsLots of others, mapcar, mapcan, and loop!Another Data Structure ‐ Arrays(make‐array listofdims) –lots of optional arguments to control aspects such as initial element(make‐array ‘(2 2)) makes a 2x2 array of any type of object (initial values are all nil), dimensions are ordered starting from 0Referring to an array element (aref arrayname dim1 dim2 …)Use setf to set the corresponding value(setq a (make‐array ‘(2 2)))(setf (aref a 0 0) 1)Input/Output(read) –reads a standard lisp object(write obj) –writes an object outCan use versions that understand escape characters (see for example, prin1, print, pprint, princ)(format dest controlstring args) –destis t for the command line, file handle otherwise, control string is a bit like a C printf string, but we use ~S (any s‐expression), ~D (integer), ~A (ascii like strings, chars), ~F (floating point), can use width values