xyzzy

Introduction

This program is about as simple as it gets. It shows what a basic program looks like, and can be used to test the compiler or interpreter.

Discussion

Simple as this program is, it illustrates some basics of Scheme syntax.

Comments

The first line in the file is a comment. Comments start in a semicolon (;) and extend to the end of the line. Their purpose is to clarify the program to a human reading it – the computer ignores them.

Procedure Calls

Procedure calls consist of a pair of paretheses enclosing the procedure name and the arguments. The first procedure call supplies one argument, the second one does not supply any arguments.

Although the above program contains one procedure call per line, it is possible to write multiple procedure calls per line, or spread one procedure call over multiple lines. The parser knows where the procedure call ends because of the parentheses.

String Literals

String literals start and end with a double quote character ("). If you want to embed a double quote character in the string, you can do so by escaping it with a backslash. A backslash can be inserted in the string by escaping it with a backslash, too. For example: "\\\"" is a string consisting of one backslash followed by one double quote. Most Scheme implementations support a broader range of escape sequences borrowed from C (e.g. \n for newline and \t for tab), but these are not defined by the standard.