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ad643cde58
Thunks are relevant when initializing attrsets and lists, passing arguments. This is an important way to produce them.
215 lines
7 KiB
C
215 lines
7 KiB
C
#ifndef NIX_API_EXPR_H
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#define NIX_API_EXPR_H
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/** @defgroup libexpr libexpr
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* @brief Bindings to the Nix language evaluator
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*
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* Example (without error handling):
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* @code{.c}
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* int main() {
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* nix_libexpr_init(NULL);
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*
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* Store* store = nix_store_open(NULL, "dummy", NULL);
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* EvalState* 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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*
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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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*
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* nix_gc_decref(NULL, value);
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* nix_state_free(state);
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* nix_store_free(store);
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* return 0;
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* }
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* @endcode
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* @{
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*/
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/** @file
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* @brief Main entry for the libexpr C bindings
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*/
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#include "nix_api_store.h"
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#include "nix_api_util.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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// cffi start
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// Type definitions
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/**
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* @brief Represents a state of the Nix language evaluator.
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*
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* Multiple states can be created for multi-threaded
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* operation.
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* @struct EvalState
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* @see nix_state_create
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*/
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typedef struct EvalState EvalState; // nix::EvalState
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/**
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* @brief Represents a value in the Nix language.
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*
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* Owned by the garbage collector.
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* @struct Value
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* @see value_manip
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*/
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typedef void Value; // nix::Value
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// Function prototypes
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/**
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* @brief Initialize the Nix language evaluator.
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*
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* This function must be called at least once,
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* at some point before constructing a EvalState for the first time.
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* This function can be called multiple times, and is idempotent.
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*
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* @param[out] context Optional, stores error information
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* @return NIX_OK if the initialization was successful, an error code otherwise.
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*/
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nix_err nix_libexpr_init(nix_c_context * context);
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/**
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* @brief Parses and evaluates a Nix expression from a string.
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*
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* @param[out] context Optional, stores error information
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* @param[in] state The state of the evaluation.
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* @param[in] expr The Nix expression to parse.
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* @param[in] path The file path to associate with the expression.
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* This is required for expressions that contain relative paths (such as `./.`) that are resolved relative to the given
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* directory.
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* @param[out] value The result of the evaluation. You must allocate this
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* yourself.
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* @return NIX_OK if the evaluation was successful, an error code otherwise.
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*/
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nix_err nix_expr_eval_from_string(
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nix_c_context * context, EvalState * state, const char * expr, const char * path, Value * value);
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/**
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* @brief Calls a Nix function with an argument.
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*
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* @param[out] context Optional, stores error information
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* @param[in] state The state of the evaluation.
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* @param[in] fn The Nix function to call.
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* @param[in] arg The argument to pass to the function.
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* @param[out] value The result of the function call.
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* @return NIX_OK if the function call was successful, an error code otherwise.
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* @see nix_init_apply() for a similar function that does not performs the call immediately, but stores it as a thunk.
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* Note the different argument order.
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*/
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nix_err nix_value_call(nix_c_context * context, EvalState * state, Value * fn, Value * arg, Value * value);
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/**
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* @brief Forces the evaluation of a Nix value.
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*
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* The Nix interpreter is lazy, and not-yet-evaluated Values can be
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* of type NIX_TYPE_THUNK instead of their actual value.
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*
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* This function converts these Values into their final type.
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*
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* @note You don't need this function for basic API usage, since all functions
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* that return a value call it for you. The only place you will see a
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* NIX_TYPE_THUNK is in the arguments that are passed to a PrimOp function
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* you supplied to nix_alloc_primop.
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*
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* @param[out] context Optional, stores error information
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* @param[in] state The state of the evaluation.
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* @param[in,out] value The Nix value to force.
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* @post value is not of type NIX_TYPE_THUNK
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* @return NIX_OK if the force operation was successful, an error code
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* otherwise.
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*/
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nix_err nix_value_force(nix_c_context * context, EvalState * state, Value * value);
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/**
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* @brief Forces the deep evaluation of a Nix value.
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*
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* Recursively calls nix_value_force
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*
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* @see nix_value_force
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* @warning Calling this function on a recursive data structure will cause a
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* stack overflow.
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* @param[out] context Optional, stores error information
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* @param[in] state The state of the evaluation.
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* @param[in,out] value The Nix value to force.
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* @return NIX_OK if the deep force operation was successful, an error code
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* otherwise.
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*/
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nix_err nix_value_force_deep(nix_c_context * context, EvalState * state, Value * value);
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/**
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* @brief Create a new Nix language evaluator state.
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*
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* @param[out] context Optional, stores error information
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* @param[in] searchPath Array of strings corresponding to entries in NIX_PATH.
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* @param[in] store The Nix store to use.
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* @return A new Nix state or NULL on failure.
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*/
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EvalState * nix_state_create(nix_c_context * context, const char ** searchPath, Store * store);
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/**
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* @brief Frees a Nix state.
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*
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* Does not fail.
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*
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* @param[in] state The state to free.
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*/
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void nix_state_free(EvalState * state);
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/** @addtogroup GC
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* @brief Reference counting and garbage collector operations
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*
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* The Nix language evaluator uses a garbage collector. To ease C interop, we implement
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* a reference counting scheme, where objects will be deallocated
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* when there are no references from the Nix side, and the reference count kept
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* by the C API reaches `0`.
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*
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* Functions returning a garbage-collected object will automatically increase
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* the refcount for you. You should make sure to call `nix_gc_decref` when
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* you're done with a value returned by the evaluator.
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* @{
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*/
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/**
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* @brief Increment the garbage collector reference counter for the given object.
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*
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* The Nix language evaluator C API keeps track of alive objects by reference counting.
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* When you're done with a refcounted pointer, call nix_gc_decref().
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*
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* @param[out] context Optional, stores error information
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* @param[in] object The object to keep alive
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*/
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nix_err nix_gc_incref(nix_c_context * context, const void * object);
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/**
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* @brief Decrement the garbage collector reference counter for the given object
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*
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* @param[out] context Optional, stores error information
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* @param[in] object The object to stop referencing
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*/
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nix_err nix_gc_decref(nix_c_context * context, const void * object);
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/**
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* @brief Trigger the garbage collector manually
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*
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* You should not need to do this, but it can be useful for debugging.
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*/
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void nix_gc_now();
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/**
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* @brief Register a callback that gets called when the object is garbage
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* collected.
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* @note Objects can only have a single finalizer. This function overwrites existing values
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* silently.
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* @param[in] obj the object to watch
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* @param[in] cd the data to pass to the finalizer
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* @param[in] finalizer the callback function, called with obj and cd
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*/
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void nix_gc_register_finalizer(void * obj, void * cd, void (*finalizer)(void * obj, void * cd));
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/** @} */
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// cffi end
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#ifdef __cplusplus
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}
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#endif
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/** @} */
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#endif // NIX_API_EXPR_H
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