An Invitation to Scheme

This section of the tour is for people who have never encountered the Scheme programming language before. We provide two small examples, and walk you through the basic operation of DrScheme. If you have seen Scheme, or plan to work through our textbook How to Design Programs (which relies heavily on DrScheme), you can skip this page. Consider the following simple mathematical function `f2c (t) = 5/9 x (t - 32)` which converts degrees in fahrenheit to degrees in centigrade. It's easy to convert this function into a Scheme program: use `define` to introduce a new definition, and put the operators in front of their operands. `(define (f2c t) (* 5/9 (- t 32)))` You should type this function into the upper half of the DrScheme window and click on the Execute button. This loads the function into the lower window, which is like an interactive calculator. To test it, you could try three familiar values: -40, 32 and 212. Whereas you would conventionally write `f2c(-40)` `f2c(32)` `f2c(212)` in Scheme you instead write `(f2c -40)` `(f2c 32)` `(f2c 212)` Try them out; see what answers you get! Your student would naturally be curious as to why DrScheme produces these values. This is where the Stepper becomes invaluable. It will display the step-by-step evaluation of the expressions. To use it, put the evaluation expressions (such as `(f2c -40)`) in the upper window, then click on the Step button. To learn more about Scheme, you should read the book, How to Design Programs. The rest of this tour will discuss specific features in the DrScheme environment.