alex-eg
dc98bb3551
C has two namespaces and the database had one. A typedef of a tag's name wiped it. Tags, i.e. struct, enum and union, share one namespace; they move to a table of their own. A name resolves the way C does: the ordinary identifier first, the tag when that leads nowhere. While resolving a typedef, the target was taken apart with cadr whatever it was, so (typedef points (¤ point 4)) reported point's fields as its own -- an array of four points claiming to be a point, and a macro reaching through it with v->x. Only a name and (struct|union|enum NAME) name a type now.
180 lines
6.3 KiB
Scheme
180 lines
6.3 KiB
Scheme
;;; The type database.
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;;;
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;;; Every named aggregate, typedef and define the semantic engine
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;;; walks past is recorded here, so that macros (or other forms) can
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;;; ask what a type is made of. That is what lets a macro generate
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;;; code from a struct's fields given nothing but its name.
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;;;
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;;; Entries are filled in as toplevel forms are processed, in order, so
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;;; a type has to be declared before the macro that asks about it.
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(import
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scheme
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(scheme base)
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(chicken base)
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srfi-1
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srfi-69)
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;;; Two namespaces: `struct point' and a `point' typedef are separate
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;;; declarations. Tags -- struct, union and enum alike -- share the
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;;; second table between them
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(define +type-db+ (make-hash-table)) ; typedefs and defines
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(define +tag-db+ (make-hash-table)) ; struct, union and enums
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(define (strip-pub form)
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(if (eq? (car form) 'pub) (cdr form) form))
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(define (comment-form? f)
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(and (pair? f) (eq? (car f) 'comment)))
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;;; Fields are written with the type last and one or more names before
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;;; it, so ((x y int) (p (* char))) describes three fields. Flatten that
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;;; into one (name type) per field, which is what a caller wants.
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(define (normalize-fields fields)
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(append-map
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(lambda (field)
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(if (comment-form? field)
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(list)
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(let ((type (last field))
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(names (drop-right field 1)))
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(map (lambda (name) (list name type)) names))))
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(remove comment-form? fields)))
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;;; ([pub] struct name (fields ...) . attrs)
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(define (aggregate-fields form)
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(let ((f (strip-pub form)))
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(if (and (pair? (cddr f)) (list? (caddr f)))
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(caddr f)
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(list))))
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(define (add-struct name form)
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(hash-table-set! +tag-db+ name
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(list 'struct name (normalize-fields (aggregate-fields form)))))
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(define (add-union name form)
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(hash-table-set! +tag-db+ name
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(list 'union name (normalize-fields (aggregate-fields form)))))
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;;; ([pub] enum name (value ...))
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(define (add-enum name form)
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(let ((f (strip-pub form)))
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(hash-table-set! +tag-db+ name
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(list 'enum name (if (and (pair? (cddr f)) (list? (caddr f)))
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(caddr f)
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(list))))))
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;;; ([pub] typedef new-name target)
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(define (add-typedef name form)
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(hash-table-set! +type-db+ name
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(list 'typedef name (last (strip-pub form)))))
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;;; (define name value ...) -- a C #define, kept so a macro can read a
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;;; compile-time constant rather than re-parse the source.
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(define (add-define name form)
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(hash-table-set! +type-db+ name
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(list 'define name (cddr (strip-pub form)))))
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(define (get-tag-info name)
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(hash-table-ref/default +tag-db+ name #f))
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;;; First look up the ordinary identifier, then tag of that id when
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;;; no ordinary one was declared, as C does
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(define (get-type-info name)
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(or (hash-table-ref/default +type-db+ name #f)
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(get-tag-info name)))
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;;; ((name type) ...) for a struct or union, #f for anything else --
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;;; including a name that was never declared. Callers give the better
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;;; error, since they know what they wanted it for.
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;;;
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;;; A typedef is followed to what it stands for, so reflection over an
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;;; alias works exactly as it does over the name it aliases.
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(define (get-fields name)
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(let ((info (resolve-type-info name)))
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(and info
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(memq (car info) '(struct union))
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(caddr info))))
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;;; Follow a typedef chain to the name it stands for. #f if NAME is
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;;; not a typedef. A typedef that leads back to itself stops rather
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;;; than spinning: nothing prevents one from being written.
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(define (get-underlying-type name)
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(let follow ((name name) (seen (list)))
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(and (not (member name seen))
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(let ((info (get-type-info name)))
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(and info
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(eq? (car info) 'typedef)
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(let ((target (caddr info)))
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(or (and (symbol? target) (follow target (cons name seen)))
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target)))))))
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;;; The declaration NAME ultimately names. For a typedef that is the
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;;; entry of whatever it stands for, and for anything else it is
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;;; NAME's own info
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(define (target-tag target)
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(cond
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((symbol? target) target)
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((and (pair? target)
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(memq (car target) '(struct union enum))
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(pair? (cdr target))
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(symbol? (cadr target)))
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(cadr target))
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(else #f)))
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(define (resolve-type-info name)
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(let ((info (resolve-ordinary-type-info name)))
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(if (and info (memq (car info) '(struct union enum)))
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info
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(or (get-tag-info name) info))))
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(define (resolve-ordinary-type-info name)
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(let ((info (get-type-info name)))
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(and info
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(if (eq? (car info) 'typedef)
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(let ((tag (target-tag (get-underlying-type name))))
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;; A typedef target is written in type position, where
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;; `struct point' means the tag
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(and tag (or (get-tag-info tag) (get-type-info tag))))
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info))))
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;;; Type matcher macro
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;;; (type-match type
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;;; (int ...)
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;;; ((* const char) ...)
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;;; ([int 10] ...)
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;;; (else ...))
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;;;
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;;; A type is a form, not an atom, so this compares with equal? rather
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;;; than dispatching like `case'. Patterns are literal types and are not
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;;; evaluated; `else' is optional and the whole thing is #f when nothing
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;;; matches and there is no else.
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(define-syntax type-match
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(syntax-rules (else)
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((_ type) #f)
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((_ type (else body ...)) (begin body ...))
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((_ type (pattern body ...) clause ...)
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(if (equal? type 'pattern)
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(begin body ...)
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(type-match type clause ...)))))
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;;; Map function to each field/value of a structure/union/enum
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;;; For enums, field-type is the type of the enum (since C 23)
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;;; (map-fields type-name
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;;; (lambda (field-name field-type) ...))
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;;;
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;;; Returns #f if nothing of that name was declared
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(define (map-fields struct-union-enum fn)
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(let ((info (resolve-type-info struct-union-enum)))
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(and info
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(case (car info)
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((struct union)
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(map (lambda (field) (fn (car field) (cadr field)))
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(caddr info)))
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;; An enumerator's type is the enum itself -- named as it was
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;; declared, since `enum some-typedef' is not a C type.
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((enum)
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(let ((type (list 'enum (cadr info))))
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(map (lambda (value) (fn value type))
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(caddr info))))
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(else #f)))))
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