21.8 Summary

In this chapter, we introduced macros by explaining their purpose as a language-extension tool, and by showing a range of Dylan macros. Macros can be useful when you want to tailor the language to express a particular problem domain more concisely.

Table 21.1 summarizes how constraints control pattern-variable matches.

Table 21.1 Pattern constraints.
Constraint	Matches
`token`	a lexeme (a Dylan word), including literal strings, symbols, and numbers and punctuation
`name`	a Dylan identifier, including reserved identifiers, such as `define`, `end`, and operators such as `+`, or `*`
`variable`	either `variable` or `variable :: <type>`, useful for macros that mimic variable binding (automatically drops the `:: <type>`, as appropriate on substitution)
`expression`	a well-formed Dylan expression — a constant, such as `37`; a variable, such as `my-position`; a function call, such as `get-current-time()`; a statement, such as `if (test) 12 else try() end`; or a binary operand series, such as `x + y * z`
`body`	a well-formed Dylan body — a sequence of semicolon-separated constituents, each constituent being either a definition, local declaration, or expression
`case-body`	a Dylan `case` statement body
`*`	any sequence of Dylan tokens and parsed forms