[erlang-bugs] try in shell

[Tony Rogvall]

On 17 sep 2014, at 00:46, Daniel Luna <daniel@REDACTED> wrote:

> The answer to your question is called f().
> 
> 
You are right, I am a fool :-)

> Your variables are bound in all future catch statements and won't match.
> 
> The errors from compilation is about the *statement*, not the full function. The statement will result in an arithmetic error even if the function won't.
> 
Well. I think that is up for an argument. The compiler is "smart" enough to see that the code will result in an arithmetic exception 
but not even smart enough to see that it is caught?
> Your third example in the shell leading to the erl_eval:expr/3 result looks like a bug in the shell though. I'm guessing that the shell strips one layer of stack trace to show the original function, but this solution leads to the wrong result when there's an extra level of indirection.
> 
> 

Hmm.

/Tony

> Regards,
> 
> Daniel
> 
> On Sep 16, 2014 6:18 PM, "Tony Rogvall" <tony@REDACTED> wrote:
> Hi!
> 
> Not sure how this is supposed to be, given that there is a shell function called catch_exception/1.
> 
> Running in 17.1 (approx)
> 
> > try throw(x) catch Class:Reason -> {Class,Reason} end.
> {throw,x}
> 
> > try exit(2) catch Class:Reason -> {Class,Reason} end.
> * exception exit: 2
> 
> > try foo:bar() catch Class:Reason -> {Class,Reason} end.
> * exception error: undefined function erl_eval:expr/3
> 
> > try 1/0 catch Class:Reason -> {Class,Reason} end.
> * exception error: an error occurred when evaluating an arithmetic expression
> 
> > try (a=b) catch Class:Reason -> {Class,Reason} end.
> * exception error: no match of right hand side value b
> 
> Putting the above try expression in a module:
> 
> -module(tryme).
> -compile(export_all).
> 
> test1() ->
>     try throw(x) catch Class:Reason -> {Class,Reason} end.
> 
> test2() ->
>     try exit(2) catch Class:Reason -> {Class,Reason} end.
> 
> test3() ->
>     try (a=b) catch Class:Reason -> {Class,Reason} end.
> 
> test4() ->
>     try 1/0 catch Class:Reason -> {Class,Reason} end.
> 
> test5() ->
>     try foo:bar() catch Class:Reason -> {Class,Reason} end.
> 
> 
> First compile:
> tryme.erl:11: Warning: no clause will ever match
> tryme.erl:14: Warning: this expression will fail with a 'badarith' exception
> 
> On line 11 there are no try clauses, but catch clauses that will always match, so the warning is a bit strange.
> And the expression on line 14 is a try, so it will never fail with badarith, possibly return an error tuple lets see:
> 
> > tryme:test1().
> {throw,x}
> > tryme:test2().
> {exit,2}
> > tryme:test3().
> {error,{badmatch,b}}
> > tryme:test4().
> {error,badarith}
> > tryme:test5().
> {error,undef}
> 
> This looks a bit more like I would expect.
> 
> Comments?
> 
> /Tony
> 
> 
> 
> 
> 
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