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Sulong supports standard Polyglot interop messages. This document explains what it does when it receives them, how to get it to explicitly send them, and what messages it sends for normal LLVM operations on foreign objects.

Detailed reference documentation of Polyglot interop support in Sulong can be found in polyglot.h (in mxbuild/sulong-libs/polyglot.h when building from source).

How Sulong responds to messages from other languages


Values created with polyglot_from_*_array behave as polyglot arrays. The size is explicitly set from the len argument.


Values created with polyglot_from_* behave as objects with named keys. Struct members are directly translated to member keys. Primitives and pointer values are readable and writable. Nested structs or arrays are only readable.


For pointers to structs (created with polyglot_from_*), the key must be a string specifying the member name of the struct. For pointers to arrays (created with polyglot_from_*_array), the key must be an integer number specifying the array index. The index will be bounds checked.

For struct members of primitive or pointer type, the READ message results in a memory read and the WRITE message results in a memory write.

For complex data types (e.g. structs within structs, or arrays of structs), the READ message will do pointer arithmetic to produce a new polyglot value representing the nested value. WRITE is not supported for complex data types.


Function pointers in Sulong respond to the EXECUTE message.

How to explicitly send messages from Sulong

You can use the built-ins defined in polyglot.h.

What messages are sent for LLVM operations on foreign objects

Foreign objects are represented as untyped pointers. The foreign objects can be accessed from Sulong using various methods:

primitive arrays

Foreign array values can be accessed by casting them to the corresponding C pointer type and accessing them. This works for primitive arrays and pointer arrays.

int *array = (int*) value;
int x = array[index];  // sends READ(index), possibly followed by UNBOX
array[index] = value;  // sends WRITE(index, value)

executable objects

Executable foreign objects can be cast to a function pointer type and called.

void (*fn)(int) = (void (*)(int)) value;
fn(5);  // sends EXECUTE

structs or arrays of structs

For accessing user-defined structs, foreign values can be converted to pointers with explicit type information.

struct MyStruct {
  int someField;


struct MyStruct *myStruct = polyglot_as_MyStruct(value);
int x = myStruct->someField;  // sends READ("someField")
myStruct->someField = 5;      // sends WRITE("someField", 5)

explicit access

Other interop messages can be sent directly using the built-ins defined in polyglot.h.