Advanced Programming Guide

26 • Chapter 2: Procedures, Variables, and Extending MapleExample 1The following application prompts the user for an answer to a question.> DetermineSign := proc(a::algebraic) local s;> printf("Is the sign of %a positive? Answer yes or no: ",a);> s := readline(terminal);> evalb( s="yes" or s = "y" );> end proc:> DetermineSign(u-1);Is the sign of u-1 positive?Answer yes or no: ytrueFor more details on the readline command, see sec-Information:tion 4.5.Reading Expressions from the TerminalYou can write procedures that interpret user input as a Maple expressionrather than a string. The readstat command reads one expression fromthe keyboard.readstat( prompt )The prompt is an optional string.> readstat("Enter degree: ");Enter degree: n-1;n − 1The user input for a readstat command must have a terminating semicolonor colon, or an error is raised.Advantages Unlike the readline command, which only reads one line,the readstat allows you to break a large expression across multiple lines.Another advantage of using the readstat command is that if there isan error in the input, the readstat command automatically repeats theprompt for user input.