13.10 Fast-Load Serialization

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▼ | 13 | Input and Output

13.1 | Ports
13.2 | Byte and String Input
13.3 | Byte and String Output
13.4 | Reading
13.5 | Writing
13.6 | Pretty Printing
13.7 | Reader Extension
13.8 | Printer Extension
13.9 | Serialization
13.10 | Fast-Load Serialization
13.11 | Cryptographic Hashing

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s-exp->fasl
fasl->s-exp

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#### 13.10`` Fast-Load Serialization🔗ℹ

(require racket/fasl) | package: base

The bindings documented in this section are provided by the racket/fasl library, not racket/base or racket.

> > procedure
> > (s-exp->fasl |  | v |
> > | [ | out |
> > |  | #:keep-mutable? keep-mutable? |
> > |  | #:handle-fail handle-fail |
> > |  | #:external-lift? external-lift? |
> > |  | #:skip-prefix? skip-prefix?]) |
> → (or/c (void) bytes?)
> v : any/c
> out : (or/c output-port? #f) = #f
> keep-mutable? : any/c = #f
> handle-fail : (or/c #f (any/c . -> . any/c)) = #f
> external-lift? : (or/c #f (any/c . -> . any/c)) = #f
> skip-prefix? : any/c = #f
> > procedure
> > (fasl->s-exp |  | in |  |  |  |
> > | [ | #:datum-intern? datum-intern? |  |  |  |
> > |  | #:external-lifts external-lifts |  |  |  |
> > |  | #:skip-prefix? skip-prefix?]) |  | → |  | any/c
> in : (or/c input-port? bytes?)
> datum-intern? : any/c = #t
> external-lifts : vector? = '#()
> skip-prefix? : any/c = #f

The s-exp->fasl function serializes v to a byte string, printing it directly to out if out is an output port or returning the byte string otherwise. The fasl->s-exp function decodes a value from a byte string (supplied either directly or as an input port) that was encoded with s-exp->fasl.

The v argument must be a value that could be quoted as a literal—that is, a value without syntax objects for which (compile `',v) would work and be readable after write—or it can include correlated objects mixed with those values. The byte string produced by s-exp->fasl does not use the same format as compiled code, however.

If a value within v is not valid as a quoted literal, and if handle-fail is not #f, then handle-fail is called on the nested value, and the result of handle-fail is written in that value’s place. The handle-fail procedure might raise an exception instead of returning a replacement value. If handle-fail is #f, then the exn:fail:contract exception is raised when an invalid value is encountered.

If external-lift? is not #f, then it receives each value v-sub encountered in v by s-exp->fasl. If the result of external-lift? on v-sub is true, then v-sub is not encoded in the result, and it instead treated as externally lifted. A deserializing fasl->s-exp receives a external-lifts vector that has one value for each externally lifted value, in the same order as passed to external-lift? on serialization.

Like (compile `',v), s-exp->fasl does not preserve graph structure, support cycles, or handle non-prefab structures. Compose s-exp->fasl with serialize to preserve graph structure, handle cyclic data, and encode serializable structures. The s-exp->fasl and fasl->s-exp functions consult current-write-relative-directory and current-load-relative-directory (falling back to current-directory), respectively, in the same way as bytecode saving and loading to store paths in relative form, and they similarly allow and convert constrained srcloc values (see Printing Compiled Code).

Unless keep-mutable? is provided as true to s-exp->fasl, then mutable values in v are replaced by immutable values when the result is decoded by fasl->s-exp. Unless datum-intern? is provided as #f, then any immutable value produced by fasl->s-exp is filtered by datum-intern-literal. The defaults make the composition of s-exp->fasl and fasl->s-exp behave like the composition of write and read.

If skip-prefix? is not #f, then a prefix that identifies the stream as a serialization is not written by s-exp->fasl or read by fasl->s-exp. Omitting a prefix can save a small amount of space, which can useful when serializing small values, but it gives up a sanity check on the fasl->s-exp that is often useful.

The byte-string encoding produced by s-exp->fasl is independent of the Racket version, except as future Racket versions introduce extensions that are not currently recognized. In particular, the result of s-exp->fasl will be valid as input to any future version of fasl->s-exp (as long as the skip-prefix? arguments are consistent).

Examples:

> > (define fasl (s-exp->fasl (list #("speed") 'racer #\!)))
> > fasl
> #"racket/fasl:\0\24\34\3 \1\23\5speed\16\5racer\r!"
> > (fasl->s-exp fasl)
> '(#("speed") racer #\!)

Changed in version 6.90.0.21 of package base: Made s-exp->fasl format version-independent and added the #:keep-mutable? and #:datum-intern? arguments.
Changed in version 7.3.0.7: Added support for correlated objects.
Changed in version 7.5.0.3: Added the #:handle-fail argument.
Changed in version 7.5.0.9: Added the #:external-lift? and #:external-lifts arguments.
Changed in version 8.9.0.4: Added support for fxvectors and flvectors.

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