External declarations (ext)

ext declares foreign symbols so Silk code can call C (or wasm imports) access foreign variables.

Full reference: ext.

Notes#

• supported ext subset + ABI notes: ext
• Embedding ABI contract: abi libsilk

Syntax#

// C function named `puts`.
ext puts = fn (string) -> i32;

// Bind a different symbol name.
ext c_malloc "malloc" = fn (i64) -> u64;
ext c_free "free" = fn (u64) -> void;

// External variable.
ext errno = i32;

Examples#

Example: call a C symbol#

import std::io;

ext puts = fn (string) -> i32;

fn main () -> int {
  puts("hello from ext");
  std::io::println("ok");
  return 0;
}

Example: opaque handle pattern (FFI-safe pointers)#

struct Thing;

ext thing_new = fn () -> &Thing;
ext thing_free = fn (&Thing) -> void;

fn main () -> int {
  let t: &Thing = thing_new();
  thing_free(t);
  return 0;
}

See also#

• Full reference: ext
• ABI details for string and optionals: abi libsilk