diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 5e2f71649..a93e531b6 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -897,6 +897,10 @@ void Value::mkStringMove(const char * s, const NixStringContext & context)
     copyContextToValue(*this, context);
 }
 
+void Value::mkPath(std::string_view path)
+{
+    mkPath(makeImmutableString(path));
+}
 
 void Value::mkPath(const SourcePath & path)
 {
diff --git a/src/libexpr/nix_api_expr.cc b/src/libexpr/nix_api_expr.cc
new file mode 100644
index 000000000..df8a66053
--- /dev/null
+++ b/src/libexpr/nix_api_expr.cc
@@ -0,0 +1,141 @@
+#include <cstring>
+#include <iostream>
+#include <stdexcept>
+#include <string>
+
+#include "config.hh"
+#include "eval.hh"
+#include "globals.hh"
+#include "util.hh"
+
+#include "nix_api_expr.h"
+#include "nix_api_expr_internal.h"
+#include "nix_api_store.h"
+#include "nix_api_store_internal.h"
+#include "nix_api_util.h"
+#include "nix_api_util_internal.h"
+
+#ifdef HAVE_BOEHMGC
+#define GC_INCLUDE_NEW 1
+#include "gc_cpp.h"
+#endif
+
+nix_err nix_libexpr_init(nix_c_context *context) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  {
+    auto ret = nix_libutil_init(context);
+    if (ret != NIX_OK)
+      return ret;
+  }
+  {
+    auto ret = nix_libstore_init(context);
+    if (ret != NIX_OK)
+      return ret;
+  }
+  try {
+    nix::initGC();
+  }
+  NIXC_CATCH_ERRS
+}
+
+Expr *nix_parse_expr_from_string(nix_c_context *context, State *state,
+                                 const char *expr, const char *path,
+                                 GCRef *ref) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    Expr *result = state->state.parseExprFromString(
+        expr, state->state.rootPath(nix::CanonPath(path)));
+    if (ref)
+      ref->ptr = result;
+    return result;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+nix_err nix_expr_eval(nix_c_context *context, State *state, Expr *expr,
+                      Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    state->state.eval((nix::Expr *)expr, *(nix::Value *)value);
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_value_call(nix_c_context *context, State *state, Value *fn,
+                       Value *arg, Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    state->state.callFunction(*(nix::Value *)fn, *(nix::Value *)arg,
+                              *(nix::Value *)value, nix::noPos);
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_value_force(nix_c_context *context, State *state, Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    state->state.forceValue(*(nix::Value *)value, nix::noPos);
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_value_force_deep(nix_c_context *context, State *state,
+                             Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    state->state.forceValueDeep(*(nix::Value *)value);
+  }
+  NIXC_CATCH_ERRS
+}
+
+State *nix_state_create(nix_c_context *context, const char **searchPath_c,
+                        Store *store) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    nix::Strings searchPath;
+    if (searchPath_c != nullptr)
+      for (size_t i = 0; searchPath_c[i] != nullptr; i++)
+        searchPath.push_back(searchPath_c[i]);
+
+    return new State{
+        nix::EvalState(nix::SearchPath::parse(searchPath), store->ptr)};
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+void nix_state_free(State *state) { delete state; }
+
+GCRef *nix_gc_ref(nix_c_context *context, void *obj) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+#if HAVE_BOEHMGC
+    return new (NoGC) GCRef{obj};
+#else
+    return new GCRef{obj};
+#endif
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+void nix_gc_free(GCRef *ref) {
+#if HAVE_BOEHMGC
+  GC_FREE(ref);
+#else
+  delete ref;
+#endif
+}
+
+void nix_gc_register_finalizer(void *obj, void *cd,
+                               void (*finalizer)(void *obj, void *cd)) {
+#ifdef HAVE_BOEHMGC
+  GC_REGISTER_FINALIZER(obj, finalizer, cd, 0, 0);
+#endif
+}
diff --git a/src/libexpr/nix_api_expr.h b/src/libexpr/nix_api_expr.h
new file mode 100644
index 000000000..90aec8d18
--- /dev/null
+++ b/src/libexpr/nix_api_expr.h
@@ -0,0 +1,176 @@
+#ifndef NIX_API_EXPR_H
+#define NIX_API_EXPR_H
+/** @file
+ * @brief Main entry for the libexpr C bindings
+ */
+
+#include "nix_api_store.h"
+#include "nix_api_util.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+// Type definitions
+/**
+ * @brief Represents a parsed nix Expression, can be evaluated into a Value.
+ *
+ * Owned by the GC.
+ */
+typedef void Expr; // nix::Expr
+/**
+ * @brief Represents a nix evaluator state.
+ *
+ * Multiple can be created for multi-threaded
+ * operation.
+ */
+typedef struct State State; // nix::EvalState
+/**
+ * @brief Represents a nix value.
+ *
+ * Owned by the GC.
+ */
+typedef void Value; // nix::Value
+/**
+ * @brief Reference for the GC
+ *
+ * Nix uses a garbage collector that may not be able to see into
+ * your stack and heap. Keep GCRef objects around for every
+ * garbage-collected object that you want to keep alive.
+ */
+typedef struct GCRef GCRef; // void*
+
+// Function propotypes
+/**
+ * @brief Initializes the Nix expression evaluator.
+ *
+ * This function should be called before creating a State.
+ * This function can be called multiple times.
+ *
+ * @param[out] context Optional, stores error information
+ * @return NIX_OK if the initialization was successful, an error code otherwise.
+ */
+nix_err nix_libexpr_init(nix_c_context *context);
+
+/**
+ * @brief Parses a Nix expression from a string.
+ *
+ * The returned expression is owned by the garbage collector.
+ * Pass a gcref to keep a reference.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] state Evaluator state.
+ * @param[in] expr The Nix expression to parse.
+ * @param[in] path The file path to associate with the expression.
+ * @param[out] ref Optional, will store a reference to the returned value.
+ * @return A parsed expression or NULL on failure.
+ */
+Expr *nix_parse_expr_from_string(nix_c_context *context, State *state,
+                                 const char *expr, const char *path,
+                                 GCRef *ref);
+
+/**
+ * @brief Evaluates a parsed Nix expression.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] state The state of the evaluation.
+ * @param[in] expr The Nix expression to evaluate.
+ * @param[in] value The result of the evaluation.
+ * @return NIX_OK if the evaluation was successful, an error code otherwise.
+ */
+nix_err nix_expr_eval(nix_c_context *context, State *state, Expr *expr,
+                      Value *value);
+
+/**
+ * @brief Calls a Nix function with an argument.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] state The state of the evaluation.
+ * @param[in] fn The Nix function to call.
+ * @param[in] arg The argument to pass to the function.
+ * @param[out] value The result of the function call.
+ * @return NIX_OK if the function call was successful, an error code otherwise.
+ */
+nix_err nix_value_call(nix_c_context *context, State *state, Value *fn,
+                       Value *arg, Value *value);
+
+/**
+ * @brief Forces the evaluation of a Nix value.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] state The state of the evaluation.
+ * @param[in,out] value The Nix value to force.
+ * @return NIX_OK if the force operation was successful, an error code
+ * otherwise.
+ */
+nix_err nix_value_force(nix_c_context *context, State *state, Value *value);
+
+/**
+ * @brief Forces the deep evaluation of a Nix value.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] state The state of the evaluation.
+ * @param[in,out] value The Nix value to force.
+ * @return NIX_OK if the deep force operation was successful, an error code
+ * otherwise.
+ */
+nix_err nix_value_force_deep(nix_c_context *context, State *state,
+                             Value *value);
+
+/**
+ * @brief Creates a new Nix state.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] searchPath The NIX_PATH.
+ * @param[in] store The Nix store to use.
+ * @return A new Nix state or NULL on failure.
+ */
+State *nix_state_create(nix_c_context *context, const char **searchPath,
+                        Store *store);
+
+/**
+ * @brief Frees a Nix state.
+ *
+ * Does not fail.
+ *
+ * @param[in] state The state to free.
+ */
+void nix_state_free(State *state);
+
+/**
+ * @brief Creates a new garbage collector reference.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] obj The object to create a reference for.
+ * @return A new garbage collector reference or NULL on failure.
+ */
+GCRef *nix_gc_ref(nix_c_context *context, void *obj);
+
+/**
+ * @brief Frees a garbage collector reference.
+ *
+ * Does not fail.
+ *
+ * @param[in] ref The reference to free.
+ */
+void nix_gc_free(GCRef *ref);
+
+/**
+ * @brief Register a callback that gets called when the object is garbage
+ * collected.
+ * @note objects can only have a single finalizer. This function overwrites
+ * silently.
+ * @param[in] obj the object to watch
+ * @param[in] cd the data to pass to the finalizer
+ * @param[in] finalizer the callback function, called with obj and cd
+ */
+void nix_gc_register_finalizer(void *obj, void *cd,
+                               void (*finalizer)(void *obj, void *cd));
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+
+#endif // NIX_API_EXPR_H
diff --git a/src/libexpr/nix_api_expr_internal.h b/src/libexpr/nix_api_expr_internal.h
new file mode 100644
index 000000000..424ca2874
--- /dev/null
+++ b/src/libexpr/nix_api_expr_internal.h
@@ -0,0 +1,17 @@
+#ifndef NIX_API_EXPR_INTERNAL_H
+#define NIX_API_EXPR_INTERNAL_H
+
+// forward declaration
+namespace nix {
+class EvalState;
+};
+
+struct State {
+  nix::EvalState state;
+};
+
+struct GCRef {
+  void *ptr;
+};
+
+#endif // NIX_API_EXPR_INTERNAL_H
diff --git a/src/libexpr/nix_api_external.cc b/src/libexpr/nix_api_external.cc
new file mode 100644
index 000000000..971a175fb
--- /dev/null
+++ b/src/libexpr/nix_api_external.cc
@@ -0,0 +1,198 @@
+#include "attr-set.hh"
+#include "config.hh"
+#include "eval.hh"
+#include "gc/gc.h"
+#include "globals.hh"
+#include "value.hh"
+
+#include "nix_api_expr.h"
+#include "nix_api_expr_internal.h"
+#include "nix_api_external.h"
+#include "nix_api_util.h"
+#include "nix_api_util_internal.h"
+#include "nix_api_value.h"
+#include "value/context.hh"
+
+#include <nlohmann/json.hpp>
+
+#ifdef HAVE_BOEHMGC
+#define GC_INCLUDE_NEW 1
+#include "gc_cpp.h"
+#endif
+
+struct nix_returned_string {
+  std::string str;
+};
+
+struct nix_printer {
+  std::ostream &s;
+};
+
+struct nix_string_context {
+  nix::NixStringContext &ctx;
+};
+
+nix_returned_string *nix_external_alloc_string(const char *c) {
+  return new nix_returned_string{c};
+}
+void nix_external_dealloc_string(nix_returned_string *str) { delete str; }
+
+nix_err nix_external_print(nix_c_context *context, nix_printer *printer,
+                           const char *c) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    printer->s << c;
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_external_add_string_context(nix_c_context *context,
+                                        nix_string_context *ctx,
+                                        const char *c) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto r = nix::NixStringContextElem::parse(c);
+    ctx->ctx.insert(r);
+  }
+  NIXC_CATCH_ERRS
+}
+
+class NixCExternalValue : public nix::ExternalValueBase {
+  NixCExternalValueDesc &desc;
+  void *v;
+
+public:
+  NixCExternalValue(NixCExternalValueDesc &desc, void *v) : desc(desc), v(v){};
+  void *get_ptr() { return v; }
+  /**
+   * Print out the value
+   */
+  virtual std::ostream &print(std::ostream &str) const override {
+    nix_printer p{str};
+    desc.print(v, &p);
+    return str;
+  }
+
+  /**
+   * Return a simple string describing the type
+   */
+  virtual std::string showType() const override {
+    std::unique_ptr<nix_returned_string> r(desc.showType(v));
+    return std::move(r->str);
+  }
+
+  /**
+   * Return a string to be used in builtins.typeOf
+   */
+  virtual std::string typeOf() const override {
+    std::unique_ptr<nix_returned_string> r(desc.typeOf(v));
+    return std::move(r->str);
+  }
+
+  /**
+   * Coerce the value to a string.
+   */
+  virtual std::string coerceToString(const nix::Pos &pos,
+                                     nix::NixStringContext &context,
+                                     bool copyMore,
+                                     bool copyToStore) const override {
+    if (!desc.coerceToString) {
+      return nix::ExternalValueBase::coerceToString(pos, context, copyMore,
+                                                    copyToStore);
+    }
+    nix_string_context ctx{context};
+    // todo: pos, errors
+    std::unique_ptr<nix_returned_string> r(
+        desc.coerceToString(v, &ctx, copyMore, copyToStore));
+    if (!r) {
+      return nix::ExternalValueBase::coerceToString(pos, context, copyMore,
+                                                    copyToStore);
+    }
+    return std::move(r->str);
+  }
+
+  /**
+   * Compare to another value of the same type.
+   */
+  virtual bool operator==(const ExternalValueBase &b) const override {
+    if (!desc.equal) {
+      return false;
+    }
+    auto r = dynamic_cast<const NixCExternalValue *>(&b);
+    if (!r)
+      return false;
+    return desc.equal(v, r->v);
+  }
+
+  /**
+   * Print the value as JSON.
+   */
+  virtual nlohmann::json
+  printValueAsJSON(nix::EvalState &state, bool strict,
+                   nix::NixStringContext &context,
+                   bool copyToStore = true) const override {
+    if (!desc.printValueAsJSON) {
+      return nix::ExternalValueBase::printValueAsJSON(state, strict, context,
+                                                      copyToStore);
+    }
+    nix_string_context ctx{context};
+    std::unique_ptr<nix_returned_string> r(
+        desc.printValueAsJSON((State *)&state, strict, &ctx, copyToStore));
+    if (!r) {
+      return nix::ExternalValueBase::printValueAsJSON(state, strict, context,
+                                                      copyToStore);
+    }
+    return nlohmann::json::parse(r->str);
+  }
+
+  /**
+   * Print the value as XML.
+   */
+  virtual void printValueAsXML(nix::EvalState &state, bool strict,
+                               bool location, nix::XMLWriter &doc,
+                               nix::NixStringContext &context,
+                               nix::PathSet &drvsSeen,
+                               const nix::PosIdx pos) const override {
+    if (!desc.printValueAsXML) {
+      return nix::ExternalValueBase::printValueAsXML(
+          state, strict, location, doc, context, drvsSeen, pos);
+    }
+    nix_string_context ctx{context};
+    desc.printValueAsXML((State *)&state, strict, location, &doc, &ctx,
+                         &drvsSeen, *reinterpret_cast<const uint32_t *>(&pos));
+  }
+
+  virtual ~NixCExternalValue() override{};
+};
+
+ExternalValue *nix_create_external_value(nix_c_context *context,
+                                         NixCExternalValueDesc *desc, void *v,
+                                         GCRef *gc) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto ret = new
+#ifdef HAVE_BOEHMGC
+        (GC)
+#endif
+            NixCExternalValue(*desc, v);
+    if (gc)
+      gc->ptr = ret;
+    return (ExternalValue *)ret;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+void *nix_get_external_value_content(nix_c_context *context, ExternalValue *b) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto r = dynamic_cast<NixCExternalValue *>((nix::ExternalValueBase *)b);
+    if (r)
+      return r->get_ptr();
+    return nullptr;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
diff --git a/src/libexpr/nix_api_external.h b/src/libexpr/nix_api_external.h
new file mode 100644
index 000000000..2bb53e349
--- /dev/null
+++ b/src/libexpr/nix_api_external.h
@@ -0,0 +1,195 @@
+#ifndef NIX_API_EXTERNAL_H
+#define NIX_API_EXTERNAL_H
+/** @file
+ * @brief libexpr C bindings dealing with external values
+ */
+
+#include "nix_api_expr.h"
+#include "nix_api_util.h"
+#include "nix_api_value.h"
+#include "stdbool.h"
+#include "stddef.h"
+#include "stdint.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+/**
+ * @brief Represents a string meant for consumption by nix.
+ */
+typedef struct nix_returned_string nix_returned_string;
+/**
+ * @brief Wraps a stream that can output multiple string pieces.
+ */
+typedef struct nix_printer nix_printer;
+/**
+ * @brief A list of string context items
+ */
+typedef struct nix_string_context nix_string_context;
+
+/**
+ * @brief Allocate a nix_returned_string from a const char*.
+ *
+ * Copies the passed string.
+ * @param[in] c The string to copy
+ * @returns A nix_returned_string*
+ */
+nix_returned_string *nix_external_alloc_string(const char *c);
+
+/**
+ * @brief Deallocate a nix_returned_string
+ *
+ * There's generally no need to call this, since
+ * returning the string will pass ownership to nix,
+ * but you can use it in case of errors.
+ * @param[in] str The string to deallocate
+ */
+void nix_external_dealloc_string(nix_returned_string *str);
+
+/**
+ * Print to the nix_printer
+ *
+ * @param[out] context Optional, stores error information
+ * @param printer The nix_printer to print to
+ * @param[in] str The string to print
+ * @returns NIX_OK if everything worked
+ */
+nix_err nix_external_print(nix_c_context *context, nix_printer *printer,
+                           const char *str);
+
+/**
+ * Add string context to the nix_string_context object
+ * @param[out] context Optional, stores error information
+ * @param[out] string_context The nix_string_context to add to
+ * @param[in] c The context string to add
+ * @returns NIX_OK if everything worked
+ */
+nix_err nix_external_add_string_context(nix_c_context *context,
+                                        nix_string_context *string_context,
+                                        const char *c);
+
+/**
+ * @brief Definition for a class of external values
+ *
+ * Create and implement one of these, then pass it to nix_create_external_value
+ * Make sure to keep it alive while the external value lives.
+ *
+ * Optional functions can be set to NULL
+ *
+ * @see nix_create_external_value
+ */
+typedef struct NixCExternalValueDesc {
+  /**
+   * @brief Called when printing the external value
+   *
+   * @param[in] self the void* passed to nix_create_external_value
+   * @param[out] printer The printer to print to, pass to nix_external_print
+   */
+  void (*print)(void *self, nix_printer *printer);
+  /**
+   * @brief Called on :t
+   * @param[in] self the void* passed to nix_create_external_value
+   * @returns a nix_returned_string, ownership passed to nix
+   */
+  nix_returned_string *(*showType)(void *self); // std::string
+  /**
+   * @brief Called on `builtins.typeOf`
+   * @param self the void* passed to nix_create_external_value
+   * @returns a nix_returned_string, ownership passed to nix
+   */
+  nix_returned_string *(*typeOf)(void *self); // std::string
+  /**
+   * @brief Called on "${str}" and builtins.toString.
+   *
+   * The latter with coerceMore=true
+   * Optional, the default is to throw an error.
+   * @param[in] self the void* passed to nix_create_external_value
+   * @param[out] c writable string context for the resulting string
+   * @param[in] coerceMore boolean, try to coerce to strings in more cases
+   * instead of throwing an error
+   * @param[in] copyToStore boolean, whether to copy referenced paths to store
+   * or keep them as-is
+   * @returns a nix_returned_string, ownership passed to nix. Optional,
+   * returning NULL will make the conversion throw an error.
+   */
+  nix_returned_string *(*coerceToString)(void *self, nix_string_context *c,
+                                         int coerceMore, int copyToStore);
+  /**
+   * @brief Try to compare two external values
+   *
+   * Optional, the default is always false.
+   * If the other object was not a Nix C external value, this comparison will
+   * also return false
+   * @param[in] self the void* passed to nix_create_external_value
+   * @param[in] other the void* passed to the other object's
+   * nix_create_external_value
+   * @returns true if the objects are deemed to be equal
+   */
+  int (*equal)(void *self, void *other);
+  /**
+   * @brief Convert the external value to json
+   *
+   * Optional, the default is to throw an error
+   * @param[in] state The evaluator state
+   * @param[in] strict boolean Whether to force the value before printing
+   * @param[out] c writable string context for the resulting string
+   * @param[in] copyToStore whether to copy referenced paths to store or keep
+   * them as-is
+   * @returns string that gets parsed as json. Optional, returning NULL will
+   * make the conversion throw an error.
+   */
+  nix_returned_string *(*printValueAsJSON)(State *, int strict,
+                                           nix_string_context *c,
+                                           bool copyToStore);
+  /**
+   * @brief Convert the external value to XML
+   *
+   * Optional, the default is to throw an error
+   * @todo The mechanisms for this call are incomplete. There are no C
+   *       bindings to work with XML, pathsets and positions.
+   * @param[in] state The evaluator state
+   * @param[in] strict boolean Whether to force the value before printing
+   * @param[in] location boolean Whether to include position information in the
+   * xml
+   * @param[out] doc XML document to output to
+   * @param[out] c writable string context for the resulting string
+   * @param[in,out] drvsSeen a path set to avoid duplicating derivations
+   * @param[in] pos The position of the call.
+   */
+  void (*printValueAsXML)(State *, int strict, int location, void *doc,
+                          nix_string_context *c, void *drvsSeen, int pos);
+} NixCExternalValueDesc;
+
+/**
+ * @brief Create an external value, that can be given to nix_set_external
+ *
+ * Pass a gcref to keep a reference.
+ * @param[out] context Optional, stores error information
+ * @param[in] desc a NixCExternalValueDesc, you should keep this alive as long
+ * as the ExternalValue lives
+ * @param[in] v the value to store
+ * @param[out] ref Optional, will store a reference to the returned value.
+ * @returns external value, owned by the garbage collector
+ * @see nix_set_external
+ */
+ExternalValue *nix_create_external_value(nix_c_context *context,
+                                         NixCExternalValueDesc *desc, void *v,
+                                         GCRef *ref);
+
+/**
+ * @brief Extract the pointer from a nix c external value.
+ * @param[out] context Optional, stores error information
+ * @param[in] b The external value
+ * @returns The pointer, or null if the external value was not from nix c.
+ * @see nix_get_external
+ */
+void *nix_get_external_value_content(nix_c_context *context, ExternalValue *b);
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+
+#endif // NIX_API_EXTERNAL_H
diff --git a/src/libexpr/nix_api_value.cc b/src/libexpr/nix_api_value.cc
new file mode 100644
index 000000000..f58500367
--- /dev/null
+++ b/src/libexpr/nix_api_value.cc
@@ -0,0 +1,439 @@
+#include "attr-set.hh"
+#include "config.hh"
+#include "eval.hh"
+#include "gc/gc.h"
+#include "globals.hh"
+#include "value.hh"
+
+#include "nix_api_expr.h"
+#include "nix_api_expr_internal.h"
+#include "nix_api_util.h"
+#include "nix_api_util_internal.h"
+#include "nix_api_value.h"
+
+#ifdef HAVE_BOEHMGC
+#define GC_INCLUDE_NEW 1
+#include "gc_cpp.h"
+#endif
+
+// Helper function to throw an exception if value is null
+static const nix::Value &check_value_not_null(const Value *value) {
+  if (!value) {
+    throw std::runtime_error("Value is null");
+  }
+  return *((const nix::Value *)value);
+}
+
+static nix::Value &check_value_not_null(Value *value) {
+  if (!value) {
+    throw std::runtime_error("Value is null");
+  }
+  return *((nix::Value *)value);
+}
+
+PrimOp *nix_alloc_primop(nix_c_context *context, PrimOpFun fun, int arity,
+                         const char *name, const char **args, const char *doc,
+                         GCRef *ref) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto fun2 = (nix::PrimOpFun)fun;
+    auto p = new
+#ifdef HAVE_BOEHMGC
+        (GC)
+#endif
+            nix::PrimOp{.name = name, .args = {}, .doc = doc, .fun = fun2};
+    if (args)
+      for (size_t i = 0; args[i]; i++)
+        p->args.emplace_back(*args);
+    if (ref)
+      ref->ptr = p;
+    return (PrimOp *)p;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+Value *nix_alloc_value(nix_c_context *context, State *state, GCRef *ref) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    Value *res = state->state.allocValue();
+    if (ref)
+      ref->ptr = res;
+    return res;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+ValueType nix_get_type(nix_c_context *context, const Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    using namespace nix;
+    switch (v.type()) {
+    case nThunk:
+      return NIX_TYPE_THUNK;
+    case nInt:
+      return NIX_TYPE_INT;
+    case nFloat:
+      return NIX_TYPE_FLOAT;
+    case nBool:
+      return NIX_TYPE_BOOL;
+    case nString:
+      return NIX_TYPE_STRING;
+    case nPath:
+      return NIX_TYPE_PATH;
+    case nNull:
+      return NIX_TYPE_NULL;
+    case nAttrs:
+      return NIX_TYPE_ATTRS;
+    case nList:
+      return NIX_TYPE_LIST;
+    case nFunction:
+      return NIX_TYPE_FUNCTION;
+    case nExternal:
+      return NIX_TYPE_EXTERNAL;
+    }
+    return NIX_TYPE_NULL;
+  }
+  NIXC_CATCH_ERRS_RES(NIX_TYPE_NULL);
+}
+
+const char *nix_get_typename(nix_c_context *context, const Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    auto s = nix::showType(v);
+    return strdup(s.c_str());
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+bool nix_get_bool(nix_c_context *context, const Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nBool);
+    return v.boolean;
+  }
+  NIXC_CATCH_ERRS_RES(false);
+}
+
+const char *nix_get_string(nix_c_context *context, const Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nString);
+    return v.string.s;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+const char *nix_get_path_string(nix_c_context *context, const Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nPath);
+    return v._path;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+unsigned int nix_get_list_size(nix_c_context *context, const Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nList);
+    return v.listSize();
+  }
+  NIXC_CATCH_ERRS_RES(0);
+}
+
+unsigned int nix_get_attrs_size(nix_c_context *context, const Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nAttrs);
+    return v.attrs->size();
+  }
+  NIXC_CATCH_ERRS_RES(0);
+}
+
+double nix_get_double(nix_c_context *context, const Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nFloat);
+    return v.fpoint;
+  }
+  NIXC_CATCH_ERRS_RES(NAN);
+}
+
+int64_t nix_get_int(nix_c_context *context, const Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nInt);
+    return v.integer;
+  }
+  NIXC_CATCH_ERRS_RES(0);
+}
+
+ExternalValue *nix_get_external(nix_c_context *context, Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nExternal);
+    return (ExternalValue *)v.external;
+  }
+  NIXC_CATCH_ERRS_NULL;
+}
+
+Value *nix_get_list_byidx(nix_c_context *context, const Value *value,
+                          unsigned int ix, GCRef *ref) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nList);
+    return (Value *)v.listElems()[ix];
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+Value *nix_get_attr_byname(nix_c_context *context, const Value *value,
+                           State *state, const char *name, GCRef *ref) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nAttrs);
+    nix::Symbol s = state->state.symbols.create(name);
+    auto attr = v.attrs->get(s);
+    if (attr) {
+      if (ref)
+        ref->ptr = attr->value;
+      return attr->value;
+    }
+    nix_set_err_msg(context, NIX_ERR_KEY, "missing attribute");
+    return nullptr;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+bool nix_has_attr_byname(nix_c_context *context, const Value *value,
+                         State *state, const char *name) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    assert(v.type() == nix::nAttrs);
+    nix::Symbol s = state->state.symbols.create(name);
+    auto attr = v.attrs->get(s);
+    if (attr)
+      return true;
+    return false;
+  }
+  NIXC_CATCH_ERRS_RES(false);
+}
+
+Value *nix_get_attr_byidx(nix_c_context *context, const Value *value,
+                          State *state, unsigned int i, const char **name,
+                          GCRef *ref) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    const nix::Attr &a = (*v.attrs)[i];
+    *name = ((const std::string &)(state->state.symbols[a.name])).c_str();
+    if (ref)
+      ref->ptr = a.value;
+    return a.value;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+nix_err nix_set_bool(nix_c_context *context, Value *value, bool b) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    v.mkBool(b);
+  }
+  NIXC_CATCH_ERRS
+}
+
+// todo string context
+nix_err nix_set_string(nix_c_context *context, Value *value, const char *str) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    v.mkString(std::string_view(str));
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_set_path_string(nix_c_context *context, Value *value,
+                            const char *str) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    v.mkPath(std::string_view(str));
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_set_double(nix_c_context *context, Value *value, double d) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    v.mkFloat(d);
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_set_int(nix_c_context *context, Value *value, int64_t i) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    v.mkInt(i);
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_set_null(nix_c_context *context, Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    v.mkNull();
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_set_external(nix_c_context *context, Value *value,
+                         ExternalValue *val) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    auto r = (nix::ExternalValueBase *)val;
+    v.mkExternal(r);
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_make_list(nix_c_context *context, State *s, Value *value,
+                      unsigned int size) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    s->state.mkList(v, size);
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_set_list_byidx(nix_c_context *context, Value *value,
+                           unsigned int ix, Value *elem) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    // todo: assert that this is a list
+    auto &v = check_value_not_null(value);
+    auto &e = check_value_not_null(elem);
+    v.listElems()[ix] = &e;
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_set_primop(nix_c_context *context, Value *value, PrimOp *p) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    v.mkPrimOp((nix::PrimOp *)p);
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_copy_value(nix_c_context *context, Value *value, Value *source) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    auto &s = check_value_not_null(source);
+    v = s;
+  }
+  NIXC_CATCH_ERRS
+}
+
+nix_err nix_set_thunk(nix_c_context *context, State *s, Value *value,
+                      Expr *expr) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    s->state.mkThunk_(v, (nix::Expr *)expr);
+  }
+  NIXC_CATCH_ERRS
+}
+
+typedef std::shared_ptr<nix::BindingsBuilder> BindingsBuilder_Inner;
+
+nix_err nix_make_attrs(nix_c_context *context, Value *value,
+                       BindingsBuilder *b) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto &v = check_value_not_null(value);
+    nix::BindingsBuilder &builder = **(BindingsBuilder_Inner *)b;
+    v.mkAttrs(builder);
+  }
+  NIXC_CATCH_ERRS
+}
+
+BindingsBuilder *nix_make_bindings_builder(nix_c_context *context, State *state,
+                                           size_t capacity) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    auto bb = state->state.buildBindings(capacity);
+    auto res = new BindingsBuilder_Inner();
+    *res = std::allocate_shared<nix::BindingsBuilder>(
+        traceable_allocator<nix::BindingsBuilder>(), bb);
+    return res;
+  }
+  NIXC_CATCH_ERRS_NULL
+}
+
+nix_err nix_bindings_builder_insert(nix_c_context *context, BindingsBuilder *b,
+                                    const char *name, Value *value) {
+  if (context)
+    context->last_err_code = NIX_OK;
+  try {
+    nix::BindingsBuilder &builder = **(BindingsBuilder_Inner *)b;
+    auto &v = check_value_not_null(value);
+    nix::Symbol s = builder.state.symbols.create(name);
+    builder.insert(s, &v);
+  }
+  NIXC_CATCH_ERRS
+}
+
+void nix_bindings_builder_unref(BindingsBuilder *bb) {
+  delete (BindingsBuilder_Inner *)bb;
+}
diff --git a/src/libexpr/nix_api_value.h b/src/libexpr/nix_api_value.h
new file mode 100644
index 000000000..5ecedefeb
--- /dev/null
+++ b/src/libexpr/nix_api_value.h
@@ -0,0 +1,355 @@
+#ifndef NIX_API_VALUE_H
+#define NIX_API_VALUE_H
+
+/** @file
+ * @brief libexpr C bindings dealing with values
+ */
+
+#include "nix_api_util.h"
+#include "stdbool.h"
+#include "stddef.h"
+#include "stdint.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+// Type definitions
+typedef enum {
+  NIX_TYPE_THUNK,
+  NIX_TYPE_INT,
+  NIX_TYPE_FLOAT,
+  NIX_TYPE_BOOL,
+  NIX_TYPE_STRING,
+  NIX_TYPE_PATH,
+  NIX_TYPE_NULL,
+  NIX_TYPE_ATTRS,
+  NIX_TYPE_LIST,
+  NIX_TYPE_FUNCTION,
+  NIX_TYPE_EXTERNAL
+} ValueType;
+
+// forward declarations
+typedef void Value;
+typedef void Expr;
+typedef struct State State;
+typedef struct GCRef GCRef;
+// type defs
+/** @brief Stores an under-construction set of bindings
+ * Reference-counted
+ * @see nix_make_bindings_builder, nix_bindings_builder_unref, nix_make_attrs
+ * @see nix_bindings_builder_insert
+ */
+typedef void BindingsBuilder;
+
+/** @brief PrimOp function
+ *
+ * Owned by the GC
+ * @see nix_alloc_primop, nix_set_primop
+ */
+typedef struct PrimOp PrimOp;
+/** @brief External Value
+ *
+ * Owned by the GC
+ * @see nix_api_external.h
+ */
+typedef struct ExternalValue ExternalValue;
+
+/** @brief Function pointer for primops
+ * @param[in] state Evaluator state
+ * @param[in] pos position of function call
+ * @param[in] args list of arguments
+ * @param[out] v return value
+ * @see nix_alloc_primop, nix_set_primop
+ */
+typedef void (*PrimOpFun)(State *state, int pos, Value **args, Value *v);
+
+/** @brief Allocate a primop
+ *
+ * Owned by the GC
+ * Pass a gcref to keep a reference.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] fun callback
+ * @param[in] arity expected amount of function arguments
+ * @param[in] name function name
+ * @param[in] args array of argument names
+ * @param[in] doc optional, documentation for this primop
+ * @param[out] ref Optional, will store a reference to the returned value.
+ * @return primop, or null in case of errors
+ * @see nix_set_primop
+ */
+PrimOp *nix_alloc_primop(nix_c_context *context, PrimOpFun fun, int arity,
+                         const char *name, const char **args, const char *doc,
+                         GCRef *ref);
+
+// Function prototypes
+
+/** @brief Allocate a Nix value
+ *
+ * Owned by the GC
+ * Pass a gcref to keep a reference.
+ * @param[out] context Optional, stores error information
+ * @param[in] state nix evaluator state
+ * @param[out] ref Optional, will store a reference to the returned value.
+ * @return value, or null in case of errors
+ *
+ */
+Value *nix_alloc_value(nix_c_context *context, State *state, GCRef *ref);
+/** @name Getters
+ */
+/**@{*/
+/** @brief Get value type
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return type of nix value
+ */
+ValueType nix_get_type(nix_c_context *context, const Value *value);
+/** @brief Get type name of value
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return type name, owned string
+ * @todo way to free the result
+ */
+const char *nix_get_typename(nix_c_context *context, const Value *value);
+
+/** @brief Get boolean value
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return true or false, error info via context
+ */
+bool nix_get_bool(nix_c_context *context, const Value *value);
+/** @brief Get string
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return string
+ * @return NULL in case of error.
+ */
+const char *nix_get_string(nix_c_context *context, const Value *value);
+/** @brief Get path as string
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return string
+ * @return NULL in case of error.
+ */
+const char *nix_get_path_string(nix_c_context *context, const Value *value);
+/** @brief Get the length of a list
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return length of list, error info via context
+ */
+unsigned int nix_get_list_size(nix_c_context *context, const Value *value);
+/** @brief Get the element count of an attrset
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return attrset element count, error info via context
+ */
+unsigned int nix_get_attrs_size(nix_c_context *context, const Value *value);
+/** @brief Get float value in 64 bits
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return float contents, error info via context
+ */
+double nix_get_double(nix_c_context *context, const Value *value);
+/** @brief Get int value
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return int contents, error info via context
+ */
+int64_t nix_get_int(nix_c_context *context, const Value *value);
+/** @brief Get external reference
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return reference to external, NULL in case of error
+ */
+ExternalValue *nix_get_external(nix_c_context *context, Value *);
+
+/** @brief Get the ix'th element of a list
+ *
+ * Pass a gcref to keep a reference.
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @param[in] ix list element to get
+ * @param[out] ref Optional, will store a reference to the returned value.
+ * @return value, NULL in case of errors
+ */
+Value *nix_get_list_byidx(nix_c_context *context, const Value *value,
+                          unsigned int ix, GCRef *ref);
+/** @brief Get an attr by name
+ *
+ * Pass a gcref to keep a reference.
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @param[in] state nix evaluator state
+ * @param[in] name attribute name
+ * @param[out] ref Optional, will store a reference to the returned value.
+ * @return value, NULL in case of errors
+ */
+Value *nix_get_attr_byname(nix_c_context *context, const Value *value,
+                           State *state, const char *name, GCRef *ref);
+
+/** @brief Check if an attribute name exists on a value
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @param[in] state nix evaluator state
+ * @param[in] name attribute name
+ * @return value, NULL in case of errors
+ */
+bool nix_has_attr_byname(nix_c_context *context, const Value *value,
+                         State *state, const char *name);
+
+/** @brief Get an attribute by index in the sorted bindings
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @param[in] state nix evaluator state
+ * @param[in] i attribute index
+ * @param[out] name will store a pointer to the attribute name
+ * @return value, NULL in case of errors
+ */
+Value *nix_get_attr_byidx(nix_c_context *context, const Value *value,
+                          State *state, unsigned int i, const char **name,
+                          GCRef *ref);
+/**@}*/
+/** @name Setters
+ */
+/**@{*/
+/** @brief Set boolean value
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] b the boolean value
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_bool(nix_c_context *context, Value *value, bool b);
+/** @brief Set a string
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] str the string, copied
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_string(nix_c_context *context, Value *value, const char *str);
+/** @brief Set a path
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] str the path string, copied
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_path_string(nix_c_context *context, Value *value,
+                            const char *str);
+/** @brief Set a double
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] d the double
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_double(nix_c_context *context, Value *value, double d);
+/** @brief Set an int
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] i the int
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_int(nix_c_context *context, Value *value, int64_t i);
+/** @brief Set null
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_null(nix_c_context *context, Value *value);
+/** @brief Set an external value
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] val the external value to set. Will be GC-referenced by the value.
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_external(nix_c_context *context, Value *value,
+                         ExternalValue *val);
+/** @brief Allocate a list
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] size size of list
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_make_list(nix_c_context *context, State *s, Value *value,
+                      unsigned int size);
+/** @brief Manipulate a list by index
+ *
+ * Don't do this mid-computation.
+ * @pre your list should be at least 'ix+1' items long
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] ix index to manipulate
+ * @param[in] elem the value to set, will be gc-referenced by the value
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_list_byidx(nix_c_context *context, Value *value,
+                           unsigned int ix, Value *elem);
+/** @brief Create an attribute set from a bindings builder
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] b bindings builder to use. Make sure to unref this afterwards.
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_make_attrs(nix_c_context *context, Value *value,
+                       BindingsBuilder *b);
+/** @brief Set primop
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] op primop, will be gc-referenced by the value
+ * @see nix_alloc_primop
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_primop(nix_c_context *context, Value *value, PrimOp *op);
+/** @brief Copy from another value
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] source value to copy from
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_copy_value(nix_c_context *context, Value *value, Value *source);
+/** @brief Make a thunk from an expr.
+ *
+ * Expr will be evaluated when the value is forced
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] expr the expr to thunk
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_set_thunk(nix_c_context *context, State *s, Value *value,
+                      Expr *expr);
+/**@}*/
+
+/** @brief Create a bindings builder
+
+* @param[out] context Optional, stores error information
+* @param[in] state nix evaluator state
+* @param[in] capacity how many bindings you'll add. Don't exceed.
+* @return owned reference to a bindings builder. Make sure to unref when you're
+done.
+*/
+BindingsBuilder *nix_make_bindings_builder(nix_c_context *context, State *state,
+                                           size_t capacity);
+/** @brief Insert bindings into a builder
+ * @param[out] context Optional, stores error information
+ * @param[in] builder BindingsBuilder to insert into
+ * @param[in] name attribute name, copied into the symbol store
+ * @param[in] value value to give the binding
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_bindings_builder_insert(nix_c_context *context,
+                                    BindingsBuilder *builder, const char *name,
+                                    Value *value);
+/** @brief Unref a bindings builder
+ *
+ * Does not fail.
+ * It'll be deallocated when all references are gone.
+ * @param[in] builder the builder to unref
+ */
+void nix_bindings_builder_unref(BindingsBuilder *builder);
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+
+#endif // NIX_API_VALUE_H
diff --git a/src/libexpr/search-path.cc b/src/libexpr/search-path.cc
index a25767496..e2c3e050a 100644
--- a/src/libexpr/search-path.cc
+++ b/src/libexpr/search-path.cc
@@ -44,7 +44,7 @@ SearchPath::Elem SearchPath::Elem::parse(std::string_view rawElem)
 }
 
 
-SearchPath parseSearchPath(const Strings & rawElems)
+SearchPath SearchPath::parse(const Strings & rawElems)
 {
     SearchPath res;
     for (auto & rawElem : rawElems)
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index 335801b34..b7b3c6434 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -328,6 +328,7 @@ public:
     }
 
     void mkPath(const SourcePath & path);
+    void mkPath(std::string_view path);
 
     inline void mkPath(InputAccessor * accessor, const char * path)
     {