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C API: add a way to throw errors from primops

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Yorick van Pelt 2023-08-28 22:19:28 +02:00 • committed by José Luis Lafuente
parent 3d79f38709
commit ab9250286a
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5 changed files with 30 additions and 21 deletions
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8
doc/external-api/README.md
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@ -58,7 +58,7 @@ Nix version: 2.17
# Writing a Nix language plug-in
In this example we add a custom primitive operation (*primop*) to `builtins`.
It will increment the argument if it is an integer and return `null` otherwise.
It will increment the argument if it is an integer and throw an error otherwise.
**plugin.c:**
```C
@ -66,18 +66,18 @@ It will increment the argument if it is an integer and return `null` otherwise.
#include <nix_api_expr.h>
#include <nix_api_value.h>
void increment(State* state, int pos, Value** args, Value* v) {
void increment(void* user_data, nix_c_context* ctx, State* state, Value** args, Value* v) {
nix_value_force(NULL, state, args[0]);
if (nix_get_type(NULL, args[0]) == NIX_TYPE_INT) {
nix_set_int(NULL, v, nix_get_int(NULL, args[0]) + 1);
} else {
nix_set_null(NULL, v);
nix_set_err_msg(ctx, NIX_ERR_UNKNOWN, "First argument should be an integer.");
}
}
void nix_plugin_entry() {
const char* args[] = {"n", NULL};
PrimOp *p = nix_alloc_primop(NULL, increment, 1, "increment", args, "Example custom built-in function: increments an integer");
PrimOp *p = nix_alloc_primop(NULL, increment, 1, "increment", args, "Example custom built-in function: increments an integer", NULL);
nix_register_primop(NULL, p);
nix_gc_decref(NULL, p);
}