Is there any special syntax for shell to editor for erlang?

Question

I am new to erlang, I have been learning to code on console/command prompt. Now I have to do the below code on editor. I need the sum of given numbers (a list [1,2,3]) with foldl/3 function.

lists:foldl(fun(X, Sum) -> X + Sum end,0,[1,2,3]). 

-module(test).
    
-export([function1/1]).
    
function1(L) ->
   L = [1,2,3],   
   lists:foldl(fun(X, Sum) -> X + Sum end, 0, L).

Pardon me for the wrong format, Please let me know the correct way to do the same thing on the editor.

Thanks in advance

Answer 1

I have been learning to code on console/command prompt.

That's not very smart, but if you like the tedium of typing stuff into the shell, have at it. If you type your code in a file, using an erlang code editor that automatically does the indenting, then compile your file, you can easily edit the file to make changes, then recompile.

Now I have to do the below code on editor.

   function1(L) ->
       L = [1,2,3],   
       lists:foldl(fun(X, Sum) -> X + Sum end, 0, L).

First, there's an obvious error in that code, namely you can only assign to a variable once. If you call that function with one argument, then the parameter variable L will be assigned the argument. Yet, on the very next line, the code tries to assign to L again. Error!

Second, you can't define a named function in the shell, however you can do almost the same thing: create an anonymous function and assign it to a variable. Here's an example:

1> F1 = fun(Data) ->                                    
1> lists:foldl(fun(X, Sum) -> X + Sum end, 0, Data)     
1> end.
#Fun<erl_eval.44.40011524>
2> F1([1, 2, 3]).                                  
6

=========

After rereading your post, it sounds like you want to convert this line in the console:

lists:foldl(fun(X, Sum) -> X + Sum end,0,[1,2,3])

into a function defined in a file. The function should take one argument, where the argument is a list of numbers that should be summed up using lists:foldl/3. Is that correct? If so, here's an example:

1. Put this code in a file named a.erl in some directory:

    -module(a).
    -export([f1/1]).
   
    f1(List) ->
         lists:foldl(
           fun(X, Sum) -> X + Sum end,
           0,
           List
         ).
   

   Note that the module name and the file name have to match.

2. In a terminal window, switch directories to the directory containing that file, e.g.

     $ cd erlang_programs
   

3. Then do this:

    ~/erlang_programs$ erl
     Erlang/OTP 24 [erts-12.0.2] [source] [64-bit] [smp:4:4] 
     [ds:4:4:10] [async-threads:1]
   
     Eshell V12.0.2  (abort with ^G)
   
     1> c(a).   <--Compiles the file named a.erl in the current directory.
     {ok,a}     <--- Or, you may get a listing of errors which must be corrected to compile the file.
   
     2> a:f1([1, 2, 3]).   
     6
   
     3> a:f1([10, 20, 30]).
     60
   

   You have to call the function using the syntax module:function.