17.1 Introduction to the compilation process

An expression in the core language is Scheme code fully expanded in which: no syntactic bindings are present; all the lexical bindings have a unique name represented by a lex gensym; all the top level lexical bindings are associated to a loc gensym used to hold the binding’s current value. The compiler is used to process:

• Full library forms and full R6RS programs the expander has transformed into library-letrec* core language forms.
• Standalone expressions from invocations of R6RS’s eval, for example read by the REPL, either in the context of a stateless environment or in the context of a stateful interactive environment.

these symbolic expressions must be compiled after correct initialisation of location gensyms for:

• All the lexical bindings defined by the boot image.
• All the lexical bindings defined by the imported libraries.
• All the bindings previously defined in the stateful interactive environment, if such was used for the expansion process.

The compiler recognises the following core language forms, whose semantics is similar to the corresponding standard language syntax:

(library-letrec* ((?lhs ?loc ?rhs) ...) ?body)
(quote ?datum)
(if ?test ?consequent ?alternate)
(set! ?lhs ?rhs)
(begin ?body0 ?body ...)
(let     ((?lhs ?rhs) ...) ?body)
(letrec  ((?lhs ?rhs) ...) ?body)
(letrec* ((?lhs ?rhs) ...) ?body)
(case-lambda (?formals ?body) ...)
(annotated-case-lambda ?annotation (?formals ?body) ...)
(lambda ?formals ?body)
(foreign-call "?function-name" ?arg ...)
(primitive ?prim)
(annotated-call ?annotation ?fun ?arg ...)
?lex
(?func ?arg ...)
(typed-expr ?expr ?core-type-name)

where: a standalone ?lex atom is a lex gensym, interpreted as reference to binding; ?lhs stands for “left–hand side” and it is a lex gensym; ?rhs stands for “right–hand side”; ?loc is a loc gensym; ?prim is a symbol representing the public name of a core lexical primitive.