feat(util/io): add helper functions for consuming IO results in C++

library/init/io.lean

@@ -30,12 +30,16 @@ In the future, we may want to give more concrete data
 like in https://doc.rust-lang.org/std/IO/enum.ErrorKind.html
 -/
 @[derive HasToString Inhabited]
-def IO.error := String
+def IO.Error := String
 
-def IO.userError (s : String) : IO.error :=
+def IO.userError (s : String) : IO.Error :=
 s
 
-abbrev IO : Type → Type := EIO IO.error
+@[export lean.io_error_to_string_core]
+def IO.Error.toString : IO.Error → String :=
+id
+
+abbrev IO : Type → Type := EIO IO.Error
 
 @[inline]
 unsafe def unsafeIO {α : Type} (fn : IO α) : Option α :=

src/kernel/environment.cpp

@@ -10,6 +10,7 @@ Author: Leonardo de Moura
 #include "runtime/sstream.h"
 #include "runtime/thread.h"
 #include "util/map_foreach.h"
+#include "util/io.h"
 #include "kernel/environment.h"
 #include "kernel/kernel_exception.h"
 #include "kernel/type_checker.h"
@@ -28,13 +29,8 @@ object* set_extension_core(object*, object*, object*);
 object* environment_set_main_module_core(object*, object*);
 object* environment_main_module_core(object*);
 
-object* mk_empty_environment(uint32 trust_lvl) {
-    object* r = mk_empty_environment_core(trust_lvl, io_mk_world());
-    if (io_result_is_error(r)) { dec(r); throw exception("error creating empty environment"); }
-    object* env = io_result_get_value(r);
-    inc(env);
-    dec(r);
-    return env;
+environment mk_empty_environment(uint32 trust_lvl) {
+    return get_io_result<environment>(mk_empty_environment_core(trust_lvl, io_mk_world()));
 }
 
 environment::environment(unsigned trust_lvl):

src/library/module.cpp

@@ -18,6 +18,7 @@ Authors: Leonardo de Moura, Gabriel Ebner, Sebastian Ullrich
 #include "runtime/hash.h"
 #include "runtime/io.h"
 #include "runtime/compact.h"
+#include "util/io.h"
 #include "util/lean_path.h"
 #include "util/buffer.h"
 #include "util/name_map.h"
@@ -204,13 +205,7 @@ def writeModule (env : Environment) (fname : String) : IO Unit := */
 object * write_module_core(object * env, object * fname, object * w);
 
 void write_module(environment const & env, std::string const & olean_fn) {
-    object * r = write_module_core(env.to_obj_arg(), mk_string(olean_fn), io_mk_world());
-    if (io_result_is_error(r)) {
-        dec_ref(r);
-        throw exception(sstream() << "failed to write module '" << olean_fn << "'");
-    } else {
-        dec_ref(r);
-    }
+    consume_io_result(write_module_core(env.to_obj_arg(), mk_string(olean_fn), io_mk_world()));
 }
 
 /*
@@ -221,16 +216,7 @@ object * import_modules_core(object * mod_names, uint32 trust_level, object * w)
 
 environment import_modules(unsigned trust_lvl, std::vector<module_name> const & imports) {
     names mods(imports.begin(), imports.end());
-    object * r = import_modules_core(mods.steal(), trust_lvl, io_mk_world());
-    if (io_result_is_error(r)) {
-        dec_ref(r);
-        io_result_show_error(r); // TODO(Leo): move to exception
-        throw exception("failed to import modules");
-    } else {
-        environment env(io_result_get_value(r), true);
-        dec_ref(r);
-        return env;
-    }
+    return get_io_result<environment>(import_modules_core(mods.steal(), trust_lvl, io_mk_world()));
 }
 
 object * environment_add_modification_core(object * env, object * mod);

src/runtime/object.h

@@ -1484,7 +1484,7 @@ inline obj_res io_mk_world() {
 inline bool io_result_is_ok(b_obj_arg r) { return cnstr_tag(r) == 0; }
 inline bool io_result_is_error(b_obj_arg r) { return cnstr_tag(r) == 1; }
 inline b_obj_res io_result_get_value(b_obj_arg r) { lean_assert(io_result_is_ok(r)); return cnstr_get(r, 0); }
-inline b_obj_arg io_result_get_error(b_obj_arg r) { lean_assert(io_result_is_error(r)); return cnstr_get(r, 0); }
+inline b_obj_res io_result_get_error(b_obj_arg r) { lean_assert(io_result_is_error(r)); return cnstr_get(r, 0); }
 void io_result_show_error(b_obj_arg r);
 void io_mark_end_initialization();
 

src/stage0/init/io.cpp

@@ -20,6 +20,9 @@ obj* l_IO_println(obj*);
 obj* l_IO_Ref_set___boxed(obj*, obj*);
 obj* l_IO_Fs_handle_isEof___at_IO_Fs_handle_readToEnd___spec__1___boxed(obj*, obj*);
 obj* l_ioOfExcept___rarg(obj*, obj*, obj*);
+namespace lean {
+obj* io_error_to_string_core(obj*);
+}
 obj* l_IO_Ref_get___rarg(obj*, obj*, obj*);
 obj* l_EState_Monad(obj*, obj*);
 obj* l_IO_Ref_swap___boxed(obj*, obj*);
@@ -32,7 +35,6 @@ obj* l_IO_Ref_swap(obj*, obj*);
 obj* l_EIO_Inhabited___rarg(obj*);
 obj* l_HasRepr_HasEval___rarg(obj*, obj*, obj*);
 obj* l_IO_Prim_Ref_swap___boxed(obj*, obj*, obj*, obj*);
-obj* l_IO_error_Inhabited;
 obj* l_IO_Fs_handle_mk(obj*, obj*);
 extern "C" obj* lean_io_prim_handle_is_eof(obj*, obj*);
 obj* l_IO_println___at_HasRepr_HasEval___spec__1___boxed(obj*, obj*);
@@ -42,6 +44,7 @@ obj* l_IO_print___boxed(obj*, obj*);
 obj* l_IO_print___at_HasRepr_HasEval___spec__2___boxed(obj*, obj*);
 obj* l_IO_Prim_iterate___at_IO_Fs_handle_readToEnd___spec__3___boxed(obj*, obj*, obj*);
 obj* l_IO_Ref_reset___rarg(obj*, obj*, obj*);
+obj* l_IO_Error_Inhabited;
 obj* l_EIO_Inhabited(obj*, obj*);
 obj* l_unsafeIO(obj*);
 obj* l_IO_Prim_iterate___at_IO_Fs_handle_readToEnd___spec__3(obj*, obj*, obj*);
@@ -64,6 +67,7 @@ obj* l_IO_Prim_Ref_get___boxed(obj*, obj*, obj*);
 extern "C" obj* lean_io_prim_get_line(obj*);
 extern "C" obj* lean_io_allocprof(obj*, obj*, obj*, obj*);
 obj* l_IO_Ref_set___rarg(obj*, obj*, obj*, obj*);
+obj* l_IO_Error_HasToString;
 obj* l_IO_print___rarg(obj*, obj*, obj*, obj*);
 obj* l_IO_userError___boxed(obj*);
 obj* l_IO_Prim_getLine___boxed(obj*);
@@ -86,7 +90,6 @@ obj* l_IO_Prim_liftIO(obj*, obj*);
 obj* l_IO_Inhabited(obj*);
 obj* l_IO_Ref_modify___rarg___lambda__2(obj*, obj*, obj*, obj*, obj*);
 obj* l_IO_Prim_handle_close___boxed(obj*, obj*);
-obj* l_IO_error_HasToString;
 obj* l_IO_Prim_handle_flush___boxed(obj*, obj*);
 obj* l_IO_println___boxed(obj*);
 obj* l_ioOfExcept(obj*, obj*);
@@ -204,7 +207,7 @@ x_3 = lean::alloc_closure(reinterpret_cast<void*>(l_EIO_Inhabited___rarg), 1, 0)
 return x_3;
 }
 }
-obj* _init_l_IO_error_HasToString() {
+obj* _init_l_IO_Error_HasToString() {
 _start:
 {
 obj* x_1; 
@@ -212,7 +215,7 @@ x_1 = lean::alloc_closure(reinterpret_cast<void*>(l_String_HasToString___boxed),
 return x_1;
 }
 }
-obj* _init_l_IO_error_Inhabited() {
+obj* _init_l_IO_Error_Inhabited() {
 _start:
 {
 obj* x_1; 
@@ -236,6 +239,14 @@ lean::dec(x_1);
 return x_2;
 }
 }
+namespace lean {
+obj* io_error_to_string_core(obj* x_1) {
+_start:
+{
+return x_1;
+}
+}
+}
 obj* _init_l_unsafeIO___rarg___closed__1() {
 _start:
 {
@@ -1733,10 +1744,10 @@ l_EIO_Monad___closed__1 = _init_l_EIO_Monad___closed__1();
 lean::mark_persistent(l_EIO_Monad___closed__1);
 l_EIO_MonadExcept___closed__1 = _init_l_EIO_MonadExcept___closed__1();
 lean::mark_persistent(l_EIO_MonadExcept___closed__1);
-l_IO_error_HasToString = _init_l_IO_error_HasToString();
-lean::mark_persistent(l_IO_error_HasToString);
-l_IO_error_Inhabited = _init_l_IO_error_Inhabited();
-lean::mark_persistent(l_IO_error_Inhabited);
+l_IO_Error_HasToString = _init_l_IO_Error_HasToString();
+lean::mark_persistent(l_IO_Error_HasToString);
+l_IO_Error_Inhabited = _init_l_IO_Error_Inhabited();
+lean::mark_persistent(l_IO_Error_Inhabited);
 l_unsafeIO___rarg___closed__1 = _init_l_unsafeIO___rarg___closed__1();
 lean::mark_persistent(l_unsafeIO___rarg___closed__1);
 l_IO_println___rarg___closed__1 = _init_l_IO_println___rarg___closed__1();

src/util/io.h

@@ -0,0 +1,39 @@
+/*
+Copyright (c) 2019 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#pragma once
+#include "runtime/exception.h"
+#include "runtime/object.h"
+#include "util/string_ref.h"
+
+namespace lean {
+object* io_error_to_string_core(object * err);
+
+template<typename T> T get_io_result(object * o) {
+    if (io_result_is_error(o)) {
+        object * err_obj = io_result_get_error(o);
+        inc(err_obj);
+        dec(o);
+        string_ref error(io_error_to_string_core(err_obj));
+        throw exception(error.to_std_string());
+    } else {
+        T r(io_result_get_value(o), true);
+        dec(o);
+        return r;
+    }
+}
+
+inline void consume_io_result(object * o) {
+    if (io_result_is_error(o)) {
+        object * err_obj = io_result_get_error(o);
+        inc(err_obj);
+        dec(o);
+        string_ref error(io_error_to_string_core(err_obj));
+        throw exception(error.to_std_string());
+    }
+    dec(o);
+}
+}