Getting started with Imalab and Scheme - PRIMA

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(define value (sin 1.0)) initialises the variable value to the sine of 1.0.(define product (* 2 5)) initialises the variable product to the result of (* 2 5)(define sum (+ 1 4.0 3.2)) initialises the variable sum to the result of (+ ...)(set! sum (+ sum product)) sets the variable sum to the value of (+ sum product). The functionset! requires that the variable is already initialised.First thing that people notice while working with scheme are the large number of parentheses in a scheme command.Function values need not necessary assigned to a variable. Often it is more convenient to feed a function result directlyas a parameter for an outer function.(sqrt (+ (* 2 2) (* 3 3))) returns the norm of the vector © .Comments: a semicolon ; comments the remainder of a line (equivalent to // in c++).4 Most frequently used scheme commands4.1 Assignment and display functions(define a 0.0) defines and initialises a global variable(begin body) encapsulates several commands to one expression.It exe-(define (funcname params) body) defines a function funcname with parameters params.cutes body on call.(set!a 4.0) sets a previously defined variable to a value.(let ((var1 init1) (var2 init2) ...) body ) same as begin but the order of the executionis guaranteed. This allows to initialises local variables recursiveley.(let* ((var1 init1) (var2 var1) ...)for the initialisation of other local variables.body) same as let, but allows to use local variables(display-l "a" " " 4.0 " n") produces a 4.00000The minus in display-l is part of the function name and not an operator. In fact, the minus in schemefunction names is used very often. It is a marker that the function is written in scheme. The minus in function namescan never be confused with the minus operator, because scheme uses the polish notation (operators are always the firstargument after a parenthesis).4.2 Other useful scheme specific functions(lambda (x) (+ x x)) This lambda expression evaluates to a procedure. When the procedure is later calledwith an actual argument, the body of the lambda expression is executed and returns its last expression. ((lambda(x) (+ x x)) 4) evaluates to 8.(for-each function alist) runs the function for each element in the list alist.(exact->inexact a) returns a as floating point number (conversion from int to double). Certain c++ functionscan require the conversion of their parameters.(inexact->exact a) returns a as integer (conversion from double to int). The value is rounded.4
(stringify obj) converts object obj to a string. Possible objects are char, int, double, but also variablesand functions that evaluate to char, int or double. stringify can be called with several parameters. Returnedis the concatenated string of all parameters.(define point (cons i j)) defines a pair (i .j).(pair?point) the type test typename? returns true.(car point) returns the car-field (the first field of the pair).(set-car! point 3) sets the car-field of point to 3.(cdr point) returns the cdr-field of point. This is the list of the last element.(set-cdr! point (list 5)) sets the cdr-field to 5.(cadr point) gets the 2nd element of point. This is equivalent to (car (cdr point)). Lists are alsopairs. You can use car to access the first element, cadr to access the second, ... , cadddr to access the fourthelement.(define clist (append alist blist)) appends the lists alist and blist and places the list inclist(list-ref alist num) returns element num of alist.(define filenames (list ))(for-each (lambda (prefix)(for-each (lambda (num)(set! filenames (append filenames (list (stringify prefix num ".ppm")))))(list 1 2 3 4)))(list "frontal" "side"))These commands produce following list ("frontal1.ppm" "frontal2.ppm" "frontal3.ppm""frontal4.ppm" "side1.ppm" "side2.ppm" "side3.ppm" "side4.ppm").4.3 I/O from/to filesI/O is done by ports. You can write or read characters from ports. A port can be connected to a file or the shell.(open-input-file filename) opens input file, returns input port(open-output-file filename) opens output file, returns output port, file is created if it does not exist.(close-input-port port) closes input port.(close-output-port port) closes output port.(display obj port) writes human readable version of object obj to port port.(write obj port) writes machine readable version of object obj to port port.(newline port) writes a newline to port.5
Page 1 and 2: Getting started with Imalab and Sch
Page 3: (quit) ends imalab. This is equival
Page 7 and 8: arguments, try (help ClassName Func
Page 9 and 10: ¨¨¨SchemeC++(define c (+ a b)) c
Page 11: Follow the instructions in exhelp.s

Getting started with Imalab and Scheme - PRIMA

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