1 Convertible: Data-Conversion Protocol
| (require file/convertible) |
The file/convertible library provides a protocol to mediate between providers of data in different possible formats and consumers of the formats. For example, a datatype that implements prop:convertible might be able to convert itself to a GIF or PDF stream, in which case it would produce data for 'gif-bytes or 'pdf-bytes requests.
Any symbol can be used for a conversion request, but the following should be considered standard:
'text —
a string for human-readable text 'gif-bytes —
a byte string containing a GIF image encoding 'png-bytes —
a byte string containing a PNG image encoding 'ps-bytes —
a byte string containing a PostScript document 'eps-bytes —
a byte string containing an Encapsulated PostScript document 'pdf-bytes —
a byte string containing a PDF document 'pdf-bytes+bounds —
a list containing a byte string and four numbers; the byte string contains a PDF document and the four numbers are sizing information for the PDF document, namely the width, height, ascent and descent in that order
(convertible? v) → boolean? v : any/c
(convert v request [default])
→
(case request [(text) (or/c string? (λ (x) (eq? x default)))] [(gif-bytes png-bytes ps-bytes eps-bytes pdf-bytes) (or/c bytes? (λ (x) (eq? x default)))] [(pdf-bytes+bounds) (or/c (list/c bytes? (and/c real? (not/c negative?)) (and/c real? (not/c negative?)) (and/c real? (not/c negative?)) (and/c real? (not/c negative?))) (λ (x) (eq? x default)))] [else any/c]) v : convertible? request : symbol? default : any/c = #f