15.1 Introduction to the expansion process

First some notes on “languages” in Vicare’s jargon:

• The expanded language is a low level Scheme–like language which is the result of the expansion process: expanding a Scheme library or program means to transform the input language into a symbolic expression in the expanded language.
• The “core language” is a low level Scheme–like language which is the input recognised by the compiler.

at present the expanded language and the core language are equal, but this might change in the future.

While discussing the expander operations, we will always refer to source code in the form of libraries. R6RS also defines top level programs; however, under Vicare:

• The process of expanding programs is almost equal to the process of expanding libraries. The differences are: a program does not export syntactic bindings; the top level body of a program intermixes definitions and expressions, while the top level body of a library separates definitions and expressions.
• The result of expanding a library is equal to the result of expanding a program.
• The output of the expander is the input of the compiler, and such input is equal when compiling a library and when compiling a program.

so if we understand how libraries are expanded, we also understand how programs are expanded.