[erlang-questions] how to make beautifulll code of this working code

[Joe Armstrong]

On Mon, Aug 10, 2015 at 8:34 PM, Roelof Wobben <r.wobben@REDACTED> wrote:
> Thanks for the tip.

My pleasure.

Another tip.

When I'm writing functions I often just write a function clause that I
know will crash. For example

date_parts(Date) ->
       L = string:tokens(Date,"-"),
       [my_to_int(I) || I <- L].

my_to_int(a) ->
    1.

Then I run this and it will crash. But the shell will print the argument that
my_to_int was called with. Then  I cut and paste this into the function head.

Often I'm not 100% sure what arguments a function will be called with, so
I just put dummy arguments a,b,c etc. that will cause the program to crash.

Then I run test cases and fix the crashing cases - so the order in
which the code is developed depends upon how it is crashing.

Its a run->crash->fix cycle. It's almost like TDD I'd call it CDD
(Crash Driven Development)

Cheers

/Joe

>
> Op 10-8-2015 om 20:29 schreef Joe Armstrong:
>
>> On Mon, Aug 10, 2015 at 6:09 PM, Roelof Wobben <r.wobben@REDACTED> wrote:
>>>
>>> Op 10-8-2015 om 17:59 schreef Garry Hodgson:
>>>>
>>>> date_parts(Date) ->
>>>>      [list_to_integer(N) || N <- string:tokens(Date,"-")].
>>>
>>>
>>> When testing I see this output:
>>>
>>> 2> dates:date_parts("2012-02-02").
>>>   ** exception error: bad argument in function list_to_integer/1 called
>>> as
>>> list_to_integer(<<"2012">>) in call from
>>> dates:'-date_parts/1-lc$^0/1-0-'/1
>>> (dates.erl, line 6)
>>
>> If you're a beginner it might be helpful to not combine function calls
>> but to write the code with intermediate variables like this:
>>
>> date_parts(Date) ->
>>        L = string:tokens(Date,"-"),
>>        [list_to_integer(I) || I <- L].
>>
>> That way you can add print statements to see what's going on
>> like this:
>>
>> date_parts(Date) ->
>>        L = string:tokens(Date,"-"),
>>        io:format("L=~p~n",[L]),
>>        [list_to_integer(I) || I <- L].
>>
>> As you become more experienced you'll omit the temporary variables
>> because you'll *know* what they should be. But when you're beginning
>> make each line of code do as little as possible and print the results to
>> check your understanding.
>>
>> Poke each line into the shell to see what's happening.
>>
>> /Joe
>>
>>
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