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102 lines
2.9 KiB
Plaintext
102 lines
2.9 KiB
Plaintext
/*
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* Copyright (c) 1995 Ernest Bowen
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* Permission is granted to use, distribute, or modify this source,
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* provided that this copyright notice remains intact.
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*
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* By: Ernest Bowen <ernie@neumann.une.edu.au>
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*/
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/*
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* Demonstration of some uses of prompt() and eval().
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*
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* adder() simulates a simple adding machine: starting with sum = 0,
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* each number entered in response to the ? prompt is added to sum
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* and the result displayed. Operation of adder() is ended by
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* entering "end", "exit" or "quit"; "end" returns to the level from
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* which adder() is called, e.g. with:
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*
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* for (;;) adder()
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*
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* entering "end" would start a new edition with sum = 0; "quit" and
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* "exit" return to the top level.
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*
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* Each response to ? is read as
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* a string terminated by a newline; the statements and expressions
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* in this string are compiled and evaluated as in function evaluation;
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* thus the string may include variables, assignments, functions, etc.
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* as in:
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*
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* 2 + 3
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* x = 2 + 3, x^3
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* x^2
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* local x = 2; while (x < 100) x *= 2; x % 100
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* x
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* exp(2, 1e-5)
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* sum
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* print sum^2;
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* 3; print sum^2;
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*
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* (Here the second line creates x as a global variable; the local
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* variable x in the fourth line has no effect on the global x. In
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* the last three lines, sum is the sum of numbers already entered, so
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* the third last line doubles the value of sum. The value returned
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* by "print sum^2;" is the null value, so the second last line adds
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* nothing to sum. The last line returns the value 3, i.e. the last
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* non-null value found for the expressions separated by semicolons,
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* so sum will be increased by 3 after the "print sum^2;" command
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* is executed. xxx The terminating semicolon is essential in the
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* last two lines. A command like eval("print 7;") is acceptable to
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* calc but eval("print 7") causes an exit from calc. xxx)
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*
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* If the value returned is not a number (e.g. the name of a list or matrix,
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* or if the string has syntax errors as in "2 + ", in which case the
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* value returned is an error value), the compile error messages and a
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* request for another number are displayed.
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*
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* Calling showvalues(str) assumes str defines a function of x as in:
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*
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* "sin(x)", "x^2 + 3*x", "exp(x, 1e-5)".
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*
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* Values of the function so defined are returned for values of x
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* entered in reponse to the ? prompt. Operation is terminated by
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* entering "end", "exit" or "quit".
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*/
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define adder() {
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global sum = 0;
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local s, t;
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for (;;) {
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s = prompt("? ");
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if (s == "end")
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break;
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t = eval(s);
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if (!isnum(t)) {
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print "Please enter a number";
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continue;
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}
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sum += t;
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print "\t":sum;
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}
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}
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global x;
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define showvalues(str) {
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local s;
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for (;;) {
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s = prompt("? ");
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if (s == "end")
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break;
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x = eval(s);
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if (!isnum(x)) {
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print "Please enter a number";
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continue;
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}
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print "\t":eval(str);
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}
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}
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if (config("lib_debug") >= 0) {
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print "adder() defined";
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print "showvalues(str) defined";
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}
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