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https://github.com/NixOS/nix.git
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74 lines
2 KiB
Markdown
74 lines
2 KiB
Markdown
# Getting started
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There are two ways to interface with nix: embedding it, or as a plugin. Embedding means you link one of the nix libraries in your program and use it from there, while being a plugin means you make a library that gets loaded by the nix evaluator, specified through a configuration option.
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# Embedding the Nix Evaluator
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These examples don't include error handling.
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See the [Handling errors](@ref errors) section for more information.
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**main.c:**
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```C
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#include <nix_api_util.h>
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#include <nix_api_expr.h>
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#include <nix_api_value.h>
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#include <stdio.h>
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int main() {
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nix_libexpr_init(NULL);
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Store* store = nix_store_open(NULL, "dummy://", NULL);
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State* state = nix_state_create(NULL, NULL, store); // empty nix path
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Value *value = nix_alloc_value(NULL, state);
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nix_expr_eval_from_string(NULL, state, "builtins.nixVersion", ".", value);
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nix_value_force(NULL, state, value);
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printf("nix version: %s\n", nix_get_string(NULL, value));
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nix_gc_decref(NULL, value);
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nix_state_free(state);
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nix_store_unref(store);
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return 0;
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}
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```
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**Usage:**
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```
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$ gcc main.c $(pkg-config nix-expr-c --libs --cflags) -o main
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$ ./main
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nix version 1.2.3
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```
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# Writing a Nix Plugin
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**plugin.c:**
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```C
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#include <nix_api_util.h>
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#include <nix_api_expr.h>
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#include <nix_api_value.h>
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void increment(State* state, int pos, Value** args, Value* v) {
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nix_value_force(NULL, state, args[0]);
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if (nix_get_type(NULL, args[0]) == NIX_TYPE_INT) {
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nix_set_int(NULL, v, nix_get_int(NULL, args[0]) + 1);
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} else {
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nix_set_null(NULL, v);
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}
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}
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void nix_plugin_entry() {
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const char* args[] = {"n", NULL};
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PrimOp *p = nix_alloc_primop(NULL, increment, 1, "increment", args, "Example nix plugin function: increments an int");
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nix_register_primop(NULL, p);
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nix_gc_decref(NULL, p);
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}
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```
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**Usage:**
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```
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$ gcc plugin.c $(pkg-config nix-expr-c --libs --cflags) -shared -o plugin.so
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$ nix --plugin-files ./plugin.so repl
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nix-repl> builtins.increment 1
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2
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```
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