I'm working on a personal project and I'm trying to get Lua to work on my embedded device.
I have my own simple file system that works with the the flash drive, and now I'm trying to use modules for the lua scripts that I run on the device.
I have edited linit.c, to make it also load the modules that are existing in the flash drive, and it works for a few modules, but for most of them it just gives me a syntax error when it parses the contents of the module. I have a lua interpreter running on my Windows machine and the code I'm writing is syntactically correct and works, and the Lua API that I use is of the same version 5.4 on the device.
These are the arguments I pass to
luaL_loadbufferx(L, luaCFunction, sizeOfModule, moduleName, "t")
where, L is the lua state, luaCFunction is the lua module wrapped in a C-style return statement, sizeOfModule, moduleName and t is selfexplanatory.
Right now luaL_loadbufferx is called in a loop for every module in my flash-drive, I have overwritten the openf function from the Lua API for these external modules.
This below is one of the examples of a module that gives me
"Syntax Error: PANIC, unprotected error in call to Lua API
[string "module"]:3: '(' expected near 'writeobj'"
File: module.lua
Contents:
function writeobj()
print('Hello World')
end
File: run.lua
Contents:
require ('module')
writeobj()
Does anyone know why this happens or did I not provide sufficient information? Please let me know.
The problem was that I thought the modules passed to the buffer had to be of the LuaToC form, i.e. "return { ...luamodule...}", but changing it to pass the module only to loadbuffer was sufficient enough because it covers the case of it not being in a C style return format.
Elixir source may be injected using Code.eval_string/3. I don't see mention of running raw Erlang code in the docs:
https://hexdocs.pm/elixir/Code.html#eval_string/3
I am coming from a Scala world in which Java objects are callable using Scala syntax, and Scala is compiled into Java and visible by intercepting the compiler output (directly generated with scalac).
I get the sense that Elixir does not provide such interoperating features, nor allow injection of custom Erlang into the runtime. Is this the case?
You can use the erlang standard library modules from Elixir, as described here or here.
For example:
def random_integer(upper) do
:rand.uniform(upper) # rand is an erlang library
end
You can also add erlang packages to your mix.exs dependencies and use them in your project, as long as these packages are published on hex or on github.
You can also use erlang and elixir code together in a project as described here.
So yeah, it's perfectly possible to call erlang code from elixir.
Vice-versa is also possible, see here for more information:
Elixir compiles into BEAM byte code (via Erlang Abstract Format). This
means that Elixir code can be called from Erlang and vice versa,
without the need to write any bindings.
Expanding what #zwippie have written:
All remote function calls (by that I mean calling function with explicitly set module/alias) are in form of:
<atom with module name>.<function name>(<arguments>)
# Technically it is the same as:
# apply(module, function_name_as_atom, [arguments])
And all "upper case module names" in Elixir are just atoms:
is_atom(Foo) == true
Foo == :"Elixir.Foo" # => true
So from Elixir viewpoint there is no difference between calling Erlang functions and Elixir functions. It is just different atom passed as the receiving module.
So you can easily call Erlang modules from Elixir. That mean that without much of the hassle you should be able to compile Erlang AST from within Elixir as well:
"rand:uniform(100)"
|> :merl.quote()
|> :erl_eval.expr(#{})
No need for any mental translation.
Additionally you can without any problems mix Erlang and Elixir code in single Mix project. With tree structure like:
.
|`- mix.exs
|`- src
| `- example.erl
`- lib
`- example.ex
Where example.erl is:
-module(example).
-export([hello/0]).
hello() -> <<"World">>.
And example.ex:
defmodule Example do
def print_hello, do: IO.puts(:example.hello())
end
You can compile project and run it with
mix run -e "Example.print_hello()"
And see that Erlang module was successfully compiled and executed from within Elixir code in the same project without problems.
One more thing to watch for when calling erlang code from elixir. erlang uses charlists for strings. When you call a erlang function that takes a string, convert the string to a charlist and convert returned string to a string.
Examples:
iex(17)> :string.to_upper "test"
** (FunctionClauseError) no function clause matching in :string.to_upper/1
The following arguments were given to :string.to_upper/1:
# 1
"test"
(stdlib 3.15.1) string.erl:2231: :string.to_upper/1
iex(17)> "test" |> String.to_charlist() |> :string.to_upper
'TEST'
iex(18)> "test" |> String.to_charlist() |> :string.to_upper |> to_string
"TEST"
iex(19)>
I had cause to check the types exported by a module, and I immediately thought "right, module_info then" but was surprised to run into a few difficulties. I found I can get the exported types from modules I compile, but not from say modules in stdlib.
My (three) questions are, how do I reliably get the exported types of a module, why are the exported types in the attributes bit of the module info on some modules, and why some modules and not others?
I discovered that if I build this module:
-module(foo).
-export([bar/0]).
-export_types([baz/0]).
bar() -> bat .
And then use foo:module_info/0, I get this:
[{exports,[{bar,0},{module_info,0},{module_info,1}]},
{imports,[]},
{attributes,[{vsn,[108921085595958308709649797749441408863]},
{export_types,[{baz,0}]}]},
{compile,[{options,[{outdir,"/tmp"}]},
{version,"5.0.1"},
{time,{2015,10,22,10,38,8}},
{source,"/tmp/foo.erl"}]}]
Great, hidden away in 'attributes' is 'export_types'. Why this is in attributes I'm not quite sure, but... whatever...
I now know this will work:
4> lists:keyfind(export_types, 1, foo:module_info(attributes)).
{export_types,[{baz,0}]}
Great. So, I now know this will work:
5> lists:keyfind(export_types, 1, ets:module_info(attributes)).
false
Ah... it doesn't.
I know there are exported types of course, if the documentation isn't good enough the ets source shows:
-export_type([tab/0, tid/0, match_spec/0, comp_match_spec/0, match_pattern/0]).
In fact the exported type information for the ets module doesn't seem to be anywhere in the module info:
6> rp(ets:module_info()).
[{exports,[{match_spec_run,2},
{repair_continuation,2},
{fun2ms,1},
{foldl,3},
{foldr,3},
{from_dets,2},
{to_dets,2},
{test_ms,2},
{init_table,2},
{tab2file,2},
{tab2file,3},
{file2tab,1},
{file2tab,2},
{tabfile_info,1},
{table,1},
{table,2},
{i,0},
{i,1},
{i,2},
{i,3},
{module_info,0},
{module_info,1},
{tab2list,1},
{match_delete,2},
{filter,3},
{setopts,2},
{give_away,3},
{update_element,3},
{match_spec_run_r,3},
{match_spec_compile,1},
{select_delete,2},
{select_reverse,3},
{select_reverse,2},
{select_reverse,1},
{select_count,2},
{select,3},
{select,2},
{select,1},
{update_counter,3},
{slot,2},
{safe_fixtable,2},
{rename,2},
{insert_new,2},
{insert,2},
{prev,2},
{next,2},
{member,2},
{match_object,3},
{match_object,2},
{match_object,1},
{match,3},
{match,2},
{match,1},
{last,1},
{info,2},
{info,1},
{lookup_element,3},
{lookup,2},
{is_compiled_ms,1},
{first,1},
{delete_object,2},
{delete_all_objects,1},
{delete,2},
{delete,1},
{new,2},
{all,0}]},
{imports,[]},
{attributes,[{vsn,[310474638056108355984984900680115120081]}]},
{compile,[{options,[{outdir,"/tmp/buildd/erlang-17.1-dfsg/lib/stdlib/src/../ebin"},
{i,"/tmp/buildd/erlang-17.1-dfsg/lib/stdlib/src/../include"},
{i,"/tmp/buildd/erlang-17.1-dfsg/lib/stdlib/src/../../kernel/include"},
warnings_as_errors,debug_info]},
{version,"5.0.1"},
{time,{2014,7,25,16,54,59}},
{source,"/tmp/buildd/erlang-17.1-dfsg/lib/stdlib/src/ets.erl"}]}]
ok
I took things to extremes now and ran this, logging the output to a file:
rp(beam_disasm:file("/usr/lib/erlang/lib/stdlib-2.1/ebin/ets.beam")).
Not that I don't consider this absurd... but anyway, it's about 5,000 lines of output, but nowhere do I find an instance of the string "tid".
Up to Erlang 18 this information is not easily available.
Dialyzer, for example, extracts it from the abstract syntax tree of the core Erlang version of a module (see e.g. dialyzer_utils:get_record_and_type_info/1 used by e.g. dialyzer_analysis_callgraph:compile_byte/5)
Regarding this part:
why are the exported types in the attributes bit of the module info on some modules, and why some modules and not others?
this is due to a bad definition in your module. The attribute should be -export_type, not -export_types. If you use the correct one (and define the baz/0 type and use it somewhere so that the module compiles), the exported types... vanish, as is expected.
I'm trying to execute a simple erlang program of adding two numbers.
I'm trying to do this in Eclipse on Ubuntu 10.04 LTS.
When i execute this program, I'm getting the error as shown below:
** exception error: undefined function add:addfunc/0
How do i go about solving this error? Thanks in advance.
This program when executed in the erlang shell is working fine. But when it comes to eclipse it's giving me this error. Not this, any program for that matter is giving me the similar error. Guess I would be missing something about the eclipse configuration.
EDIT:
Anyways, This is the sample add program,
-module(add).
-export([addfunc/0]).
addfunc() ->
5 + 6.
This message tells you that module add doesn't have an exported function addfunc/0.
Ensure the function you want to be called has exactly that name, doesn't expect any
parameters, is
exported, the module is
compiled, the search path includes the compiled beam file and that there is no module clashes using code:clash()
Update
It's not clear how erlide (eclipse erlang plug-in you seem to use) compiles and runs a program. Try to compile source using erlc or inside erl shell. That way you'll have much easier controllable environment and you'll better understand what's going on.
I got exactly the same problem -for a tail recursive fibonacci function- below:
-module(math2).
-export([fibonacci/1]).
fibonacci(0) -> 0;
fibonacci(1) -> 1;
fibonacci(M) -> fibonacci(M-1) + fibonacci(M-2).
In the end, had realized that this is a compile-time exception. Then, have opened a new tab on my shell and tried with erlc, instead of erl.
$ erlc math2.erl
Now I am also able to see math2.beam file created.
Called fibonacci with 10:
4> math2:fibonacci(10).
55
and it worked!
I think you have not compiled the code and you are trying to run the program.
In eclipse, using the "Run" icon, trigger the run; which will get you to the erl shell in the console window.
There you do -
cd("C:\Learning_ERL\src").
And you should see output like-
(Learning-ERL#DALAKSHM-MNFSM)7> cd("C:\Learning_ERL\src").
c:/Learning_ERL/src
ok
Then compile the code -
c(add)
you should see something like this on the erl shell-
(Learning-ERL#DALAKSHM-MNFSM)10> c(add).
{ok,add}
Now you should be seeing a new file called - add.beam in the same directory as that of your erl source file - add.erl
add.beam is a bytecode file
Now you should be able to run the program without any error
How do you try to execute your code?
In your editor, right-click and choose "Run as"->"Erlang application". The VM that is launched will have your project loaded automatically and when editing/saving a file it will get reloaded. When launching, a console appears and you can call your code from there.
If it still doesn't work, what message do you get for m(add).?