Function value_force 

pub unsafe extern "C" fn value_force(
    context: *mut c_context,
    state: *mut EvalState,
    value: *mut value,
) -> err

@brief Forces the evaluation of a Nix value. @ingroup value_create

The Nix interpreter is lazy, and not-yet-evaluated values can be of type NIX_TYPE_THUNK instead of their actual value.

This function mutates such a nix_value, so that, if successful, it has its final type.

@param[out] context Optional, stores error information @param[in] state The state of the evaluation. @param[in,out] value The Nix value to force. @post value is not of type NIX_TYPE_THUNK @return NIX_OK if the force operation was successful, an error code otherwise.