examples/lua: Add REPL.

This example add a module thats starts an interactive READ-EVAL-
PRINT-LOOP written in Lua.

examples/lua_REPL/Makefile

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+APPLICATION = lua_repl
+
+# If no BOARD is found in the environment, use this default:
+BOARD ?= native
+
+# This has to be the absolute path to the RIOT base directory:
+RIOTBASE ?= $(CURDIR)/../..
+
+BOARD_INSUFFICIENT_MEMORY := bluepill calliope-mini cc2650-launchpad \
+                             cc2650stk maple-mini microbit nrf51dongle \
+                             nucleo-f030r8 nucleo-f031k6 nucleo-f042k6 \
+                             nucleo-f070rb nucleo-f072rb nucleo-f103rb \
+                             nucleo-f302r8 nucleo-f303k8 nucleo-f334r8 \
+                             nucleo-f410rb nucleo-l031k6 nucleo-l053r8 \
+                             opencm904 spark-core stm32f0discovery \
+                             stm32mindev airfy-beacon  arduino-mkr1000 \
+                             arduino-mkrfox1200 arduino-mkrzero arduino-zero \
+                             b-l072z-lrwan1  cc2538dk ek-lm4f120xl  feather-m0 \
+                             ikea-tradfri limifrog-v1 mbed_lpc1768  nrf6310 \
+                             nucleo-f091rc  nucleo-l073rz  nz32-sc151 \
+                             openmote-cc2538  pba-d-01-kw2x  remote-pa \
+                             remote-reva remote-revb samd21-xpro  saml21-xpro \
+                             samr21-xpro seeeduino_arch-pro  slstk3401a \
+                             sltb001a slwstk6220a sodaq-autonomo \
+                             sodaq-explorer  stk3600  stm32f3discovery \
+                             yunjia-nrf51822
+
+BOARD_BLACKLIST := arduino-duemilanove arduino-mega2560 arduino-uno \
+                   chronos hifive1 jiminy-mega256rfr2 mega-xplained mips-malta \
+                   msb-430 msb-430h pic32-clicker pic32-wifire telosb \
+                   waspmote-pro wsn430-v1_3b wsn430-v1_4 z1
+
+# Comment this out to disable code in RIOT that does safety checking
+# which is not needed in a production environment but helps in the
+# development process:
+DEVELHELP ?= 1
+
+# Uncomment the following lines to enable debugging features.
+#CFLAGS_OPT = -Og
+#CFLAGS += -DDEBUG_ASSERT_VERBOSE -DLUA_DEBUG
+
+# Change this to 0 show compiler invocation lines by default:
+QUIET ?= 1
+
+# This value is in excess because we are not sure of the exact requirements of
+# lua (see the package's docs). It must be fixed in the future by taking
+# appropriate measurements.
+CFLAGS += -DTHREAD_STACKSIZE_MAIN='(THREAD_STACKSIZE_DEFAULT+7000)'
+
+USEPKG += lua
+
+include $(RIOTBASE)/Makefile.include
+
+# The code below generates a header file from any .lua scripts in the
+# example directory. The header file contains a byte array of the
+# ASCII characters in the .lua script.
+
+LUA_PATH := $(BINDIR)/lua
+
+# add directory of generated *.lua.h files to include path
+CFLAGS += -I$(LUA_PATH)
+
+# generate .lua.h header files of .lua files
+LUA = $(wildcard *.lua)
+
+LUA_H := $(LUA:%.lua=$(LUA_PATH)/%.lua.h)
+
+$(LUA_PATH)/:
+	@mkdir -p $@
+
+# FIXME: This way of embedding lua code is not robust. A proper script will
+#        be included later.
+
+$(LUA_H): | $(LUA_PATH)/
+$(LUA_H): $(LUA_PATH)/%.lua.h: %.lua
+	xxd -i $< | sed 's/^unsigned/const unsigned/g' > $@
+
+$(RIOTBUILD_CONFIG_HEADER_C): $(LUA_H)

examples/lua_REPL/README.md

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+## Lua interactive interpreter
+
+### About
+
+This example shows how to run a [Lua](https://www.lua.org/) Read-Eval-Print loop.
+It works in a similar way to the lua shell that comes with your operating
+system's default lua installation.
+
+
+### How to run
+
+Type `make all flash` to program your board. The lua interpreter communicates
+via UART (like the shell).
+
+It is not recommended to use `make term` because the default RIOT terminal messes
+up the input and output and the REPL needs multi-line input. Instead, use something
+like `miniterm.py` from pyserial:
+
+```
+miniterm.py --eol LF --echo /dev/ttyACM0 115200
+```
+
+By default only some of the builtin modules are loaded, to preserve RAM. See
+the definition of `BARE_MINIMUM_MODS` in main.c.
+
+### Using the interpreter
+
+See the [Lua manual](https://www.lua.org/manual/5.3/) for the syntax of the language.
+
+Each piece of single or multi-line input is compiled as a chunk and run. For this
+reason, issuing "local" definitions may not work as expected: the definitions
+will be local to that chunk only.

examples/lua_REPL/main.c

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+/*
+ * Copyright (C) 2018 Freie Universität Berlin.
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     examples
+ * @{
+ *
+ * @file
+ * @brief       Lua shell in RIOT
+ *
+ * @author      Juan Carrano <j.carrano@fu-berlin.de>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include "lua_run.h"
+#include "lua_builtin.h"
+#include "repl.lua.h"
+
+/* The basic interpreter+repl needs about 13k ram AT Minimum but we need more
+ * memory in order to do interesting stuff.
+ */
+#define MAIN_LUA_MEM_SIZE (40000)
+
+static char lua_memory[MAIN_LUA_MEM_SIZE] __attribute__ ((aligned(__BIGGEST_ALIGNMENT__)));
+
+#define BARE_MINIMUM_MODS (LUAR_LOAD_BASE | LUAR_LOAD_IO | LUAR_LOAD_CORO | LUAR_LOAD_PACKAGE)
+
+const struct lua_riot_builtin_lua _lua_riot_builtin_lua_table[] = {
+    { "repl", repl_lua, sizeof(repl_lua) }
+};
+
+
+const struct lua_riot_builtin_lua *const lua_riot_builtin_lua_table = _lua_riot_builtin_lua_table;
+
+const size_t lua_riot_builtin_lua_table_len = 1;
+
+int main(void)
+{
+    printf("Using memory range for Lua heap: %p - %p, %zu bytes\n",
+           lua_memory, lua_memory + MAIN_LUA_MEM_SIZE, sizeof(void *));
+
+    while (1) {
+        int status, value;
+        puts("This is Lua: starting interactive session\n");
+
+        status = lua_riot_do_module("repl", lua_memory, MAIN_LUA_MEM_SIZE,
+                                    BARE_MINIMUM_MODS, &value);
+
+        printf("Exited. status: %s, return code %d\n", lua_riot_strerror(status),
+               value);
+    }
+
+    return 0;
+}

examples/lua_REPL/repl.lua

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+--[[
+   @file repl.lua
+   @brief   Read-eval-print loop for LUA
+   @author  Juan Carrano <j.carrano@fu-berlin.de>
+   Copyright (C) 2018 Freie Universität Berlin. Distributed under the GNU Lesser General Public License v2.1.
+]]
+
+local _R_EVAL = 0
+local _R_CONT = 1
+local _R_EXIT = 2
+local _R_ERROR = 3
+
+--[[ Read code from standard input (whatever stdin means for lua)
+    @return action_code     what the eval loop should do
+    @return code_or_msg     either code (_R_EVAL) or a message (_R_ERROR) or nil
+                            (_R_CONT, _R_EXIT).
+]]
+
+local function re()
+    io.write("L> ")
+    io.flush()
+    local ln = io.read()
+
+    if not ln then
+        return _R_EXIT
+    elseif ln == "\n" then
+        return _R_CONT
+    end
+    -- Try to see if we have an expression
+    local maybe_code, compile_err = load("return "..ln)
+    -- Try to see if we have a single-line statement
+    if not maybe_code then
+        maybe_code, compile_err = load(ln)
+    end
+    -- Try a multiline statement
+    if not maybe_code then
+        -- It's not really necessary to use a coroutine, but it shows that they
+        -- work.
+        local _get_multiline = coroutine.create(
+            function ()
+                coroutine.yield(ln.."\n")   -- We already have the first line of input
+                while 1 do
+                    io.write("L.. ")
+                    io.flush()
+                    local l = io.read()
+                    if #l ~= 0 then
+                        l = l.."\n"
+                    end
+                    coroutine.yield(l)
+                end
+            end
+            )
+        local get_multiline = function()
+                local a, b = coroutine.resume(_get_multiline)
+                if a then
+                    return b
+                else
+                    return nil
+                end
+            end
+
+        maybe_code, compile_err = load(get_multiline)
+    end
+
+    if not maybe_code then
+        return _R_ERROR, compile_err
+    else
+        return _R_EVAL, maybe_code
+    end
+end
+
+local function repl()
+    io.write("Welcome to the interactive interpreter\n");
+
+    while 1 do
+        local action, fn_or_message = re()
+
+        if action == _R_EVAL then
+            local success, msg_or_ret = pcall(fn_or_message)
+            if not success then
+                print("Runtime error", msg_or_ret)
+            elseif msg_or_ret ~= nil then
+                print(msg_or_ret)
+            end
+        elseif action == _R_EXIT then
+            print()
+            return
+        elseif action == _R_ERROR then
+            print("Compile error:", fn_or_message)
+        end -- (action == _R_CONT) : do nothing
+    end
+end
+
+repl()