A token may be surrounded by whitespace and comments. Identifiers, numbers, characters, and dot are delimited by whitespace, a comment beginning with a semicolon, an open or close parenthesis, an open or close square bracket, or a string quote. Spacing between items within a production appears for readability only and should be treated as if it were not present. Wherever matching open and close parentheses appear, matching open and close square brackets may be used instead, except within the syntax for vectors. A program consists of a sequence of definitions and expressions.
Derived definitions are syntactic extensions that expand into some form of definition.
A transformer expression is an expression that evaluates to a transformer. Derived expressions include all other nondefinition syntactic forms described in this book, plus syntactic extensions that expand into some form of expression. Identifiers may denote variables, keywords, module names, or symbols, depending upon context. They are formed from sequences of letters, digits, and special characters. With three exceptions, standard identifiers cannot begin with a character that can also begin a number, i.e., they cannot begin with .