Preserver previous command results (avoid rerunning commands)

[owen2345]

Features

• feat: support to print previous command result with __ or __previous_result
• feat: Preserve regular command results as serialized values and make them available to be used by next commands (avoid re running commands)
• feat: Scan declared variables inside a command to make available in next commands

TODO:

• Add tests
• Calculate all variables declared inside the command (currently only takes the first variable using regex)

Samples:

  $> 10 # => 10
  $> puts "previous result: #{__}" # => previous result: 10

  $> var1 = "Var1" # => ""
  $> puts "var1 is: #{var1}" # => var1 is: Var1

  # Array support
  $> arr = [1,2,3]
  $> puts "arr result: #{arr} and size: #{arr.size}" # => arr result: [1, 2, 3] and size: 3

  # Hash support
  $> hash = { s: "String", number: 10 }
  $> puts "result: #{hash} and number: #{hash["number"]}" # => result: {s: "String", number: 10} and number: 10

  #complex objects (Amber app)
  $> require "./config/application.cr"
  $> qty_articles = Article.count
  $> article = Article.create(title: "Article 1")
  $> puts "qty_articles is #{qty_articles} vs #{Article.count}" # qty_articles is 0 vs 1
  $> puts "last article is: #{article.title}" # last article is: Article 1

Status: In progress

[jwoertink]

Well this is interesting! I'll come back to review a bit later, but my first question is what is the difference between _p and __ (two underscores we currently use)?

[owen2345]

Well difference between _p and __ is that __ can not be used as a variable in the next command, against _p which can be used as a normal variable like:

puts "previous value: #{_p}" 

Btw: I tried to replace _p into __ but unfortunately crystal does not accept as a valid variable name, either _;

[jwoertink]

__ can not be used as a variable in the next command

I'm not sure that I follow exactly. I know this works in Crystal

__ = 1

__ += 1

puts __

Here's the PR where it was added in originally #63

I just want to make sure that if we're making this change, it's not a 1 to 1 of what we have now for the sake of "a better name" or something along those lines. I'd rather not have 2 ways to do this, so if we're going to add in _p, then we should remove __ with an explanation as to why _p is a better solution. Hope that makes sense.

[owen2345]

@jwoertink you were right! Sorry my mistake. I was too tired yesterday then I could not test it very well.

[jwoertink]

No worries! I just want to make sure we're getting this right. Thanks for contributing ❤️

[jwoertink]

Sorry it took me some time to come back and review this. It seems like a pretty decent start. I was able to create a time object and it persisted between calls which is an amazing improvement. It looks like there's still some issues though.

For example:

icr(1.0.0) > t = Time.utc

 => 2021
icr(1.0.0) > t

 => 2021
icr(1.0.0) > t.to_s("%F")

 => "2021-06-14"

It seems the default output of a Time object is just the year which could be a bit confusing.

Trying to use both __ and __previous_result just return this error:

icr(1.0.0) > __
Showing last frame. Use --error-trace for full trace.

In .icr_Vbx6IjLdROuGGOgDEDzfUA.cr:14:3

 14 | __previous_result = (__previous_result);
      ^
Error: expression has no effect
icr(1.0.0) > __previous_result
Showing last frame. Use --error-trace for full trace.

In .icr_Vbx6IjLdROuGGOgDEDzfUA.cr:14:3

 14 | __previous_result = (__previous_result);
      ^
Error: expression has no effect

Lastly, trying to define a simple class in two lines seems to bork the whole session:

icr(1.0.0) > class Test
icr(1.0.0) >   end
There was a problem expanding macro 'macro_4538303136'

Code in macro 'init'

 1 | {% if T < Enum %}
     ^
Called macro defined in macro 'init'

 1 | {% if T < Enum %}

Which expanded to:

 > 422 |       when .== Class then new Class
 > 423 |
 > 424 |       when .== GC:Module then new GC:Module
                          ^
Error: unexpected token: Module (expecting ',', ';' or '

')

After doing that, no other command works until I quit and restart.

Overall I think this will be an amazing update, but I think it'll need just a bit more fine tuning before we merge it in.

Ping me if you have any questions, or need anymore testing done. Thanks for your work on this!