12.2.6 Values associated to symbols

Unsafe Operation: $symbol-value sym

Unsafe Operation: $set-symbol-value! sym val

The value field has multiple purposes:

• When sym is the unique identifier of a data structure type: the value field holds the RTD of the data structure.
• When sym is a label gensym associated to a syntactic binding exported by the boot image: value holds the syntactic binding descriptor.
• When sym is a label gensym associated to a syntactic binding imported in the current lexical environment: value holds the syntactic binding descriptor.
• When sym is a fresh symbol returned by a call to gensym: we can use this field for any purpose we want.

Notice that this field is initialised to the unbound object, so we can test the value of a newly created symbols with:

($unbound-object? ($symbol-value? sym))

Unsafe Operation: $unbound-object? obj

Return #t if obj is the special unbound machine word value, otherwise return #f.

Unsafe Operation: $symbol-proc sym

Unsafe Operation: $set-symbol-proc! sym proc

Accessor and mutator for the field proc.

Unsafe Operation: $set-symbol-value/proc! sym val

Set both the fields value and proc of sym to val.

Unsafe Operation: $init-symbol-function! sym proc

Still to be documented.