• Print one object at a "deep" level with values set at every level above

  cue eval ./stages/prd/regions/... -e envoy
  

• Print object at a SPECIFIC level

  cue eval ./stages/prd/regions/envoy.cue -e envoy
  

• Check yaml against cue

  cue vet ranges.yaml check.cue
  

• Vet Cue (give it the deepest level. It wont traverse down itself)

  cue vet -c --strict ./stages/prd/regions/...
  

• Format

  cue fmt ./...
  

• Render YAML

package main

import (
	"encoding/yaml"
	"tool/cli"
)

command: dump: {
	task: print: cli.Print & {
		text: yaml.Marshal(_rendered)
	}
}

cue cmd dump ./main/...

• YAML
  • https://github.com/cue-lang/cue/blob/v0.7.0/doc/tutorial/kubernetes/README.md
  • cue import -f -R foo.yaml

• incomplete value string: - you are missing a concrete value somewhere. yaml.Marshal is EXTREMELY finicky. You will want to pull whatever out of yaml.Marshal() into a thing that you can run via cue eval. Look for places where you don't have concrete values. Those ALL need fixed.

• We create a debug/ directory at the same level as the package we are trying to debug or "simulate". Then, we symlink all .cue files that DON'T include yaml.Marshal(..).

mkdir debug && cd debug
ln -snf ../main/debug.cue .
ln -snf ../main/modify.cue .

Then, we can debug Cue via the following

cue eval ./debug/... -e '_debug'

And, we can still render/test marshalling the same cue to yaml with

cue cmd dump ./main/...

1. Define the interface you want users to use FIRST.
2. Define the input schema --- with constraints and defaults
   • Don't try to rely directly on the output schema for the input schema too
   • I ran into a lot of pain doing this
3. Define the output schema --- with contstraints and defaults. Use defaults generously --- you want (or need) to produce
4. Define transformation "functions" via the function pattern

• Mental model

  • Think merging multi-level (or layered) value maps (JSON objects) without overrides
  • "Objects" think "Go Structs"
  • Schemas can have constraints and default values
  • Packages are like Go package i.e., keep domains, etc. packaged
  • Types and values are one and the same (for loops, etc)
  • Order of evaluation does not matter
  • In global packages, set defaults, DON'T set concrete values (in most cases)
    • No such thing as "overwriting" at a deeper level
  • You take the type and constraints, but cant overwrite once a value becomes concrete
  • Types - https://cuetorials.com/overview/types-and-values/

• Project Structure

  • https://alpha.cuelang.org/docs/concept/modules-packages-instances/#instances
  • Within a module, all .cue files with the same package name are part of the same package.
  • A package is evaluated within the context of a certain directory.
  • Within this context, only the files belonging to that package in that directory and its ancestor directories within the module are combined.
  • We call that an instance of a package.
    • "fully-compiled, concrete data-structure of the package in this 'instance'" when you reference this
  • module root: schema
    • all policy
  • medial directories: policy
    • some policy
  • leaf directories: data
    • all data

• Have the Cue playground open to test minimal examples out
  • https://cuelang.org/play
• Cue Stdlib - https://pkg.go.dev/cuelang.org/go/pkg

• https://cuelang.org/docs/concepts/logic/
• https://alpha.cuelang.org/docs/howto/
• https://cuetorials.com/overview/foundations/

• Pattern matching / avoiding switch - https://cuetorials.com/overview/types-and-values/#pattern-matching-constraints

• Enums - https://cuelang.org/docs/tutorials/tour/types/disjunctions/

• Defining "global" package variable for re-use in the package - https://alpha.cuelang.org/docs/howto/use-the-built-in-function-or/

• Aliases - https://alpha.cuelang.org/docs/language-guide/templating/references/#aliases

• List comprehension / for-each - https://alpha.cuelang.org/docs/language-guide/templating/comprehensions/

• Applying constraint to many fields at once - https://alpha.cuelang.org/docs/language-guide/templating/constructing-maps/#pattern-constraints

• "one of" / either x OR y

  • Reference - https://cuetorials.com/patterns/fields/#oneof
  • Example - https://cuelang.org/play/?id=NIrmjj_gM4Z#cue@export@cue

cue eval ./oneOf/...

• debug

cue eval ./debug/... -e _debug

• "if not set" or "bottom"

  • Reference - https://cuelang.org/docs/tutorials/tour/types/bottom/

cue eval ./bottom/... -e output

set:                  "a"
notSet:               "im explicitly setting here"
notSetButWithDefault: "default"

• Read a raw file and write it somewhere

  • Reference - https://pkg.go.dev/cuelang.org/go/pkg/tool/file

cue cmd "read_file" ./read_file