# Portable Foreign Function Interface for R7RS schemes
Foreign function interface that is supported on multiple R7RS Sceheme implementations.
Any help in form of constructive advice and bug reports are appreciated.
[Project](https://todo.sr.ht/~retropikzel/r7rs-pffi)
[Issue trackers](https://sr.ht/~retropikzel/r7rs-pffi/trackers)
[Maling lists](https://sr.ht/~retropikzel/r7rs-pffi/lists)
[Jenkins](https://jenkins.scheme.org/job/r7rs_pffi/job/r7rs-pffi/)
## Table of contents
- [Goals](#goals)
- [Non Goals](#non-goals)
- [Status](#status)
- [Implementation status](#implementation-status)
- [Implementation table](#implementation-table)
- [Other Implementations](#other-implementations)
- [Documentation](#documentation)
- [Usage](#usage)
- [Chibi](#usage_chibi)
- [Chicken](#usage_chicken)
- [Racket](#usage_racket)
- [Kawa](#usage_kawa)
- [Reference](#reference)
- [Types](#types)
- [Procedures and macros](#procedures-and-macros)
- [pffi-init](#strongpffi-initstrong)
- [pffi-size-of](#strongpffi-size-ofstrong-type--gt-number)
- [pffi-align-of](#strongpffi-align-ofstrong-type--gt-number)
- [pffi-shared-object-auto-load](#strongpffi-shared-object-auto-loadstrong)
- [pffi-shared-object-load](#strongpffi-shared-object-loadstrong-headers-path)
- [pffi-pointer-null](#strongpffi-pointer-nullstrong--gt-pointer)
- [pffi-pointer-null?](#strongpffi-pointer-nullstrong-pointer--gt-boolean)
- [pffi-pointer-allocate](#strongpffi-pointer-allocatestrong-size--gt-pointer)
- [pffi-pointer?](#strongpffi-pointerstrong-object--gt-boolean)
- [pffi-pointer-free](#strongpffi-pointer-freestrong-pointer)
- [pffi-pointer-set!](#strongpffi-pointer-setstrong-pointer-type-offset-value)
- [pffi-pointer-get](#strongpffi-pointer-getstrong-pointer-type-offset--gt-object)
- [pffi-string->pointer](#strongpffi-string-gtpointerstrong-string--gt-pointer)
- [pffi-pointer->string](#strongpffi-pointer-gtstringstrong-pointer--gt-string)
- [pffi-struct-make](#strongpffi-struct-makestrong-name-members--pointer--gt-pffi-struct)
- [pffi-struct-pointer](#strongpffi-struct-pointerstrong-pffi-struct--gt-pointer)
- [pffi-struct-offset-get](#strongpffi-struct-offset-getstrong-member-name--gt-number)
- [pffi-struct-get](#strongpffi-struct-getstrong-pffi-struct-member-name--gt-object)
- [pffi-struct-set!](#strongpffi-struct-setstrong-pffi-struct-member-name-value)
- [pffi-define](#strongpffi-definestrong-scheme-name-shared-object-c-name-return-type-argument-types)
- [pffi-define-callback](#strongpffi-define-callbackstrong-scheme-name-return-type-argument-types-procedure)
## Goals
- Support only R7RS implementations
- Same interface on all implementations
- Some things that are procedures on one implementation are macros on other,
but they must behave the same
- Stability and being boring after 1.0.0 is reached
## Non goals
- To have every possible FFI feature
- Compiling of used library C code at any point
- That is no stubs, no C code generated by the library and so on
- The pffi library itself may require compilation on installation
## Status
Currently the interface of the library is in okay shape. It propably will not change much but no
guarantees are being made just yet.
Due to supporting many different Scheme implementations, different parts of this software are in
different stage. As a whole it is still in **alpha** stage. That said the interface should not be
changing anymore and some implementations are in **beta**.
### Current caveats
- No way to pass structs by value
- Most implementations are missing callback support
## Implementation table
### Beta
| | pffi-init | pffi-size-of | pffi-shared-object-auto-load | pffi-shared-object-load | pffi-pointer-null | pffi-pointer-null? | pffi-pointer-allocate | pffi-pointer-address | pffi-pointer? | pffi-pointer-free | pffi-pointer-set! | pffi-pointer-get | pffi-string->pointer | pffi-pointer->string | pffi-struct-make | pffi-struct-pointer | pffi-struct-offset-get | pffi-struct-get | pffi-struct-set! | pffi-define | pffi-define-callback |
|--------------|-----------|--------------|------------------------------|-------------------------|-------------------|--------------------|-----------------------|----------------------|---------------|-------------------|-------------------|------------------|----------------------|----------------------|------------------|---------------------|------------------------|-----------------|------------------|-------------|----------------------|
| Chibi | X | X | X | X | X | X | X | X | X | X | X | X | X | X | X | X | X | X | X | X | |
| Gauche | X | X | X | X | X | X | X | | X | X | X | X | X | X | X | X | X | X | X | X | |
| Guile | X | X | X | X | X | X | X | | X | X | X | X | X | X | X | X | X | X | X | X | X |
| Racket | X | X | X | X | X | X | X | | X | X | X | X | X | X | X | X | X | X | X | X | X |
| Saggittarius | X | X | X | X | X | X | X | | X | X | X | X | X | X | X | X | X | X | X | X | X |
### Alpha
| | pffi-init | pffi-size-of | pffi-shared-object-auto-load | pffi-shared-object-load | pffi-pointer-null | pffi-pointer-null? | pffi-pointer-allocate | pffi-pointer-address | pffi-pointer? | pffi-pointer-free | pffi-pointer-set! | pffi-pointer-get | pffi-string->pointer | pffi-pointer->string | pffi-struct-make | pffi-struct-pointer | pffi-struct-offset-get | pffi-struct-get | pffi-struct-set! | pffi-define | pffi-define-callback |
|--------------|-----------|--------------|------------------------------|-------------------------|-------------------|--------------------|-----------------------|----------------------|---------------|-------------------|-------------------|------------------|----------------------|----------------------|------------------|---------------------|------------------------|-----------------|------------------|-------------|----------------------|
| Chicken-5 | X | X | X | X | X | X | X | | X | X | X | X | X | X | X | X | X | X | X | X | X |
| Cyclone | X | X | X | X | X | X | X | | X | X | X | X | X | X | X | X | X | X | X | X | |
| Gambit | X | X | | | | | | X | | | | | | | X | X | X | X | X | | |
| Gerbil | X | | | | | | | | | | | | | | X | X | X | X | X | | |
| Larceny | X | | | | | | | | | | | | | | X | X | X | X | X | | |
| Mosh | X | X | X | X | X | X | X | | X | X | X | X | X | X | X | X | X | X | X | X | X |
| Skint | X | | | | | | | | | | | | | | X | X | X | X | X | | |
| Stklos | X | X | X | X | X | X | X | | X | X | | | | | X | X | X | X | X | | |
| tr7 | | | | | | | | | | | | | | | X | X | X | X | X | | |
| Ypsilon | | | | | | | | | | | | | | | X | X | X | X | X | | |
### Not started
- [LIPS](https://lips.js.org/)
- Will work on nodejs by using some C FFI library from npm
- Javascript side needs design
- [Biwascheme](https://www.biwascheme.org/)
- Will work on nodejs by using some C FFI library from npm
- Javascript side needs design
- [MIT-Scheme](https://www.gnu.org/software/mit-scheme/)
- Need to study the implementation more
- [Airship](https://gitlab.com/mbabich/airship-scheme)
- Need to study the implementation more
- [Other gambit targets](https://gambitscheme.org/)
- Gambit compiles to different targets other than C too, for example Javascript. It would be cool
and interesting to see if this FFI could also support some of those
- When LIPS and Biwascheme Javascript side is done then Gambit should be done too
- [s48-r7rs](https://codeberg.org/prescheme/s48-r7rs)
- Need to study the implementation more
- [prescheme](https://codeberg.org/prescheme/prescheme)
- Need to study the implementation more
### Other
- [s7](https://scheme.fail://ccrma.stanford.edu/software/snd/snd/s7.html)
- Propably does not need FFI as it is embeddable only
- [Loko](https://scheme.fail/)
- Desires no C interop, I can respect that
## Documentation
### Usage
#### Chibi
Needs libffi-dev, on Debina/Ubuntu/Mint install with:
apt install libffi-dev
Build with:
chibi-ffi retropikzel/r7rs-pffi/r7rs-pffi-chibi.stub
gcc -o retropikzel/r7rs-pffi/r7rs-pffi-chibi.so -fPIC -shared retropikzel/r7rs-pffi/r7rs-pffi-chibi.c -lchibi-scheme -lffi
#### Chicken
Needs [r7rs egg](https://wiki.call-cc.org/eggref/5/r7rs), install with:
chicken-install r7rs
#### Racket
Needs [racket-r7rs](https://github.com/lexi-lambda/racket-r7rs), install with:
raco pkg install --auto r7rs
#### Kawa
Kawa Needs at least Java version 22
Needs jvm flags:
- --add-exports java.base/jdk.internal.foreign.abi=ALL-UNNAMED
- --add-exports java.base/jdk.internal.foreign.layout=ALL-UNNAMED
- --add-exports java.base/jdk.internal.foreign=ALL-UNNAMED
- --enable-native-access=ALL-UNNAMED
### Reference
#### Types
Types are given as symbols, for example 'int8 or 'pointer.
- int8
- uint8
- int16
- uint16
- int32
- uint32
- int64
- uint64
- char
- unsigned-char
- short
- unsigned-short
- int
- unsigned-int
- long
- unsigned-long
- float
- double
- pointer
- callback
- Callback function
#### Procedures and macros
Some of these are procedures and some macros, it might also change implementation to implementation.
##### **pffi-init**
Always call this first, on most implementation it does nothing but some implementations might need
initialisation run.
##### **pffi-size-of** object -> number
Returns the size of the pffi-struct, pffi-enum or pffi-type.
##### **pffi-align-of** type -> number
Returns the align of the type.
##### **pffi-shared-object-auto-load** headers shared-object-name [options] -> object
Load given shared object automatically searching many predefined paths.
Takes as argument a list of C headers, these are for the compiler ones. And an shared-object name,
used by the dynamic FFI's. The name of the shared object should not contain suffix like .so or
.dll. Nor should it contain any prefix like "lib".
Additional options argument can be provided, theys should be a pair with a
keyword. The options are:
- additional-versions
- Search for additional versions of shared object, given shared object "c" and additional
versions "6" "7" on linux the files "libc", "libc.6", "libc.7" are searched for.
- Can be either numbers or strings
- additional-paths
- Give additional paths to search shared objects for
Example:
(define libc-stdlib
(cond-expand
(windows (pffi-shared-object-auto-load (list "stdlib.h") "ucrtbase"))
(else (pffi-shared-object-auto-load (list "stdlib.h")
"c"
'(additional-versions . ("6"))
'(additional-search-paths . ("."))))))
##### **pffi-shared-object-load** headers path [options]
It is recommended to use the pffi-shared-object-auto-load instead of this
directly.
Headers is a list of strings needed to be included, for example
(list "curl/curl.h")
Path is the full path of the shared object without any "lib" prefix or ".so/.dll" suffix. For example:
"curl"
Options:
- additional-versions
- List of different versions of library to try, for example (list ".0" ".1")
##### **pffi-pointer-null** -> pointer
Returns a new NULL pointer.
##### **pffi-pointer-null?** pointer -> boolean
Returns #t if given pointer is null pointer, #f otherwise.
##### **pffi-pointer-allocate** size -> pointer
Returns newly allocated pointer of given size.
##### **pffi-pointer?** object -> boolean
Returns #t if given object is pointer, #f otherwise.
##### **pffi-pointer-free** pointer
Frees given pointer.
##### **pffi-pointer-set!** pointer type offset value
Sets the value on a pointer on given offset. For example:
(define p (pffi-pointer-allocate 128))
(pffi-pointer-set! p 'int 64 100)
Would set the offset of 64, on pointer p to value 100.
##### **pffi-pointer-get** pointer type offset -> object
Gets the value from a pointer on given offset. For example:
(define p (pffi-pointer-allocate 128))
(pffi-pointer-set! p 'int 64 100)
(pffi-pointer-get p 'int 64)
> 100
##### **pffi-string->pointer** string -> pointer
Makes pointer out of a given string.
##### **pffi-pointer->string** pointer -> string
Makes string out of a given pointer.
##### **pffi-struct-make** c-type members . pointer -> pffi-struct
Creates a new pffi-struct and allocates pointer for it. The members argument is a list of member
names and types. For example:
(define color (pffi-struct-make 'color '((int8 . r) (int8 . g) (int8 . b) (int8 .a ))))
(define test (pffi-struct-make "struct test" '((int8 . r) (int8 . g) (int8 . b) (int8 .a ))))
C-type argument can be symbol or a string.
##### **pffi-struct-pointer** pffi-struct -> pointer
Returns the pointer that holds the struct content. You need to use this when passing a struct as
a pointer to foreign functions.
(define s (pffi-struct-make 'test '((int . r) (int . g) (int . b))))
(pffi-struct-pointer s)
##### **pffi-struct-offset-get** member-name -> number
Returns the offset of a struct member with given name.
##### **pffi-struct-get** pffi-struct member-name -> object
Returns the value of the givens struct member.
##### **pffi-struct-set!** pffi-struct member-name value
Sets the value of the givens struct member. It is up to you to make sure that the type of value is
correct.
##### **pffi-define** scheme-name shared-object c-name return-type argument-types
Defines a new foreign function to be used from Scheme code. For example:
(define libc-stdlib
(cond-expand
(windows (pffi-shared-object-auto-load (list "stdlib.h") (list) "ucrtbase" (list "")))
(else (pffi-shared-object-auto-load (list "stdlib.h") (list) "c" (list "" "6")))))
(pffi-define c-puts libc-stdlib 'puts 'int (list 'pointer))
(c-puts "Message brought to you by FFI!")
##### **pffi-define-callback** scheme-name return-type argument-types procedure
Defines a new Sceme function to be used as callback to C code. For example:
; Load the shared library
(define libc-stdlib
(cond-expand
(windows (pffi-shared-object-auto-load (list "stdlib.h") (list) "ucrtbase" (list "")))
(else (pffi-shared-object-auto-load (list "stdlib.h") (list) "c" (list "" "6")))))
; Define C function that takes a callback
(pffi-define qsort libc-stdlib 'qsort 'void (list 'pointer 'int 'int 'callback))
; Define our callback
(pffi-define-callback compare
'int
(list 'pointer 'pointer)
(lambda (pointer-a pointer-b)
(let ((a (pffi-pointer-get pointer-a 'int 0))
(b (pffi-pointer-get pointer-b 'int 0)))
(cond ((> a b) 1)
((= a b) 0)
((< a b) -1)))))
; Create new array of ints to be sorted
(define array (pffi-pointer-allocate (* (pffi-size-of 'int) 3)))
(pffi-pointer-set! array 'int (* (pffi-size-of 'int) 0) 3)
(pffi-pointer-set! array 'int (* (pffi-size-of 'int) 1) 2)
(pffi-pointer-set! array 'int (* (pffi-size-of 'int) 2) 1)
(display array)
(newline)
;> (3 2 1)
; Sort the array
(qsort array 3 (pffi-size-of 'int) compare)
(display array)
(newline)
;> (1 2 3)