yamlscript 2024-05-21 | Slack Archive

Ingy döt Net02:05:53

I've been musing on what makes YAML a pretty good data syntax to write a programming language like YS in... When I started this project, my hopes for YAML being a reasonable syntax were pretty low. I started porting Clojure code to various made up YAML forms to see what I liked and what I didn't. To my pleasant surprise, it started looking pretty good. I've being thinking... could something similar be done in JSON, EDN or something else? If it came down to one thing, I'd give credit to YAML's "plain scalars" (unquoted strings), and the ability to use them vs the other scalar styles (quoted and literal). No other plain text data language that I know of has this (unquoted strings). To go a bit further, 3 of the other 4 scalar styles (single quoted, double quoted, and literal (heredoc semantics) play a big part in the language. Various scalar styles with various (code mode) semantics...

say: hello         # hello is a symbol here
say: 'hello'
say: "hello $name"
say: |
  hello $name,

  How are you?

The YAML spec asks you to not consider differences in scalar style (except for plain vs non-plain) when making a YAML data loader. YS is implemented as a specialized YAML loader, but it is loading data into a Clojure AST, not a data structure. In the example above, all the mapping keys are the same. YAML doesn't support a data model with duplicate keys, but again that (an AST) is not our targeted data model for this loader (the YS compiler).

🙌 1

Daniel Craig21:05:56

Suppose I have a block of cloudformation configuration that I want to template, which contains a variable expansion such as ${ENV} that I want to expand, is there a way to do this in Yamlscript? Could I perhaps drop into code mode in the middle of my data here?

--- !yamlscript/v0/

&cloudformationBlock
dataStream: 
    Type: AWS::Kinesis::Stream
    Properties:
        Name: ${ENV}_DATA_STREAM
        RetentionPeriodHours: 24
        ShardCount: 1

--- !yamlscript/v0

defn main():
    ENV =: 'dev'
    say: *cloudformationBlock

👀 1

Ingy döt Net21:05:59

sec

Ingy döt Net22:05:50

There are many ways to do this with YS. Here's one: cf.ys:

--- !yamlscript/v0/

=>:
  ENV =: 'dev'

dataStream:
  Type: AWS::Kinesis::Stream
  Properties:
    Name:: "$(=> ENV)_DATA_STREAM"
    RetentionPeriodHours: 24
    ShardCount: 1

cmd:

ys -Y cf.ys > cf.yaml

cf.yaml

dataStream:
  Type: AWS::Kinesis::Stream
  Properties:
    Name: dev_DATA_STREAM
    RetentionPeriodHours: 24
    ShardCount: 1

Ingy döt Net22:05:44

note that "$(=> ENV)_DATA_STREAM" can be "${ENV}_DATA_STREAM" in 0.1.59 when that drops

Ingy döt Net22:05:00

code already in main

Ingy döt Net22:05:34

Here's slightly different approach that you might like better: cf.ys:

--- !yamlscript/v0/

=>:
  data =: load('vars.yaml')

dataStream:
  Type: AWS::Kinesis::Stream
  Properties:
    Name:: "$(data.ENV)_DATA_STREAM"
    RetentionPeriodHours: 24
    ShardCount: 1

vars.yaml:

ENV: dev

Ingy döt Net22:05:45

does same thing

Daniel Craig22:05:11

This is really great!

Ingy döt Net22:05:49

or... cf.ys:

--- !yamlscript/v0/

dataStream:
  Type: AWS::Kinesis::Stream
  Properties:
    Name:: "$(ENV.'MY_ENV_LEVEL')_DATA_STREAM"
    RetentionPeriodHours: 24
    ShardCount: 1

cmd:

MY_ENV_LEVEL=dev ys -Y cf.ys > cf.yaml

Ingy döt Net22:05:52

🙂

Ingy döt Net22:05:06

for completeness, you can put vars in a previous document in the same file and access them with $$: cf.ys:

---
level: dev

--- !yamlscript/v0/
dataStream:
  Type: AWS::Kinesis::Stream
  Properties:
    Name:: "$($$.level)_DATA_STREAM"
    RetentionPeriodHours: 24
    ShardCount: 1

Ingy döt Net22:05:22

I was a bit confused at first because you named your var ENV which is a global mapping variable containing the environment in YS...

😁 1

Ingy döt Net22:05:29

Also I doubt Name: dev_DATA_STREAM is the end result you would want, but now you know some ways to get whatever it is you want.

Ingy döt Net22:05:11

I haven't used cloudformation but it's on my list to show how YS can help it.

Ingy döt Net22:05:38

Let me know if you need more help.

Daniel Craig22:05:53

Thanks!

Ingy döt Net22:05:04

Also look at https://github.com/BetterThanTomorrow/calva/pull/2511

Ingy döt Net22:05:47

it's a complete YS refactoring of a 650 line circleci yaml file, that turned out really well

Daniel Craig22:05:57

This is motivated by my interest in alternatives to the Serverless framework

Ingy döt Net22:05:09

URL?

Daniel Craig22:05:11

https://www.serverless.com is going to change with v4.0 and will begin charging money it seems

Ingy döt Net22:05:31

I see

Daniel Craig22:05:48

I imagine that many people & companies will be interested in alternatives to the Serverless framework

Ingy döt Net22:05:58

never heard of it until now

Daniel Craig22:05:31

It’s pretty popular but there are some things that it’s not very good at, like as a small example you have to use a plugin to get if/then/else in your Serverless yaml

Daniel Craig22:05:40

Cloudformation compiled with yamlscript would be like totally free to do programmatic things

2024-05-21

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