[erlang-questions] Programmatic interface to the shell

[Éric Pailleau]

Hello Joe,  

In bottom of this code

https://github.com/erlang/otp/blob/maint/lib/observer/src/observer_procinfo.erl

Is a simple io server, thanks to Dan Gudmunson.
This may help ?
Regards 


Le 10 août 2015 19:08, Joe Armstrong <erlang@REDACTED> a écrit :
>
> Wonderful - thanks 
>
> The main problem now is that the error messages are not exactly the same 
> as in the shell. 
>
> ie: The above code for X/0 says 
>
> > Send(P, "X/0."). 
> ** exception error: an error occurred when evaluating an arithmetic expression 
>
> But X/0. in the shell says: 
>
> > X/0. 
> ** exception error: an error occurred when evaluating an arithmetic expression 
>      in operator  '/'/2 
>         called as 4 / 0 
>
> Do you have any idea how to dig out the error message so it's exactly the same? 
>
> I'm asking because I'm writing a tutorial in a "markdown like" language 
> and I want to automate production of examples :-) 
>
>
> Thanks again 
>
> /Joe 
>
>
>
>
>
>
>
> On Mon, Aug 10, 2015 at 6:23 PM, Fred Hebert <mononcqc@REDACTED> wrote: 
> > On 08/10, Joe Armstrong wrote: 
> >> 
> >> Hello, 
> >> 
> >> Is there a *simple* programmatic interface to the Erlang shell? 
> >> 
> >> I'd like a module "shell_interface" that works like this: 
> >> 
> >>      Pid = shell_interface:new_shell(), 
> >> 
> >> Returns a new process that behaves like the Erlang shell 
> >> 
> >>      OutStr = shell_interface:eval(Pid, InStr) 
> >> 
> > 
> > Short answer is no. The Erlang shell in the `shell' module asks for 
> > information via the IO protocol and pulls it in, rather than you pushing it 
> > out. 
> > 
> > There's ways to inject yourself in there, but it's not simple. 
> > 
> >> This behaves like the Erlang shell. InStr should be what I typed into the 
> >> shell. OutStr should be what the shell replied. 
> >> 
> >> For this purpose we can assume that InStr represents a complete 
> >> sequence of expressions. 
> >> 
> > 
> > This sounds more like an evaluator/interpreter: 
> > 
> >    1> {ok, Tokens, _} = erl_scan:string("X + 4 * lists:sum([1,2,3,4])."). 
> >    ... 
> >    2> {ok, [Form]} = erl_parse:parse_exprs(Tokens). 
> >    ... 
> >    3> Bindings = erl_eval:add_binding('X', 17, erl_eval:new_bindings()). 
> >    [{'X',17}] 
> >    4> {value, Value, _} = erl_eval:expr(Form, Bindings). 
> >    {value,57,[{'X',17}]} 
> >    5> Value. 
> >    57 
> > 
> > With these basic forms it becomes doable to write a mini-shell the way you'd 
> > like it. 
> > 
> >    Eval = fun EvalLoop(Bindings) -> 
> >        receive 
> >            {cmd, Caller, Ref, String} -> 
> >                try 
> >                    {ok, Tokens, _} = erl_scan:string(String), 
> >                    %% many forms can be comma-separated 
> >                    {ok, Forms} = erl_parse:parse_exprs(Tokens), 
> >                    %% eval individually 
> >                    {value, Val, NewBindings} = erl_eval:exprs(Forms, 
> > Bindings), 
> >                    Caller ! {ok, Ref, Val}, 
> >                    EvalLoop(NewBindings) 
> >                catch 
> >                    T:R -> 
> >                        Caller ! {raise, Ref, T, R}, 
> >                        EvalLoop(Bindings) 
> >                end 
> >        end end. 
> > 
> >    Send = fun(Pid, String) -> 
> >        Ref = erlang:monitor(process, Pid), 
> >        Pid ! {cmd, self(), Ref, String}, 
> >        receive 
> >            {ok, Ref, Value} -> Value; 
> >            {raise, Ref, T, R} -> erlang:T(R) 
> >        end end. 
> > 
> >    18> P = spawn(fun() -> Eval([]) end). 
> >    <0.62.0> 
> >    19> Send(P, "X=2+2."). 
> >    4 
> >    20> Send(P, "X*X."). 
> >    16 
> >    21> Send(P, "X/0."). 
> >    ** exception error: an error occurred when evaluating an arithmetic 
> > expression 
> >    22> Send(P, "X."). 
> >    4 
> > 
> > And there  you have an evaluator. It doesn't support all the stuff like 
> > 'h().' and whatnot, but is close enough otherwise. 
> > 
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