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Any sufficiently complicated configuration language contains an ad hoc, informally-specified, bug-ridden, slow implementation of a Turing complete programming l

by jasim 9y ago

Any sufficiently complicated configuration language contains an ad hoc, informally-specified, bug-ridden, slow implementation of a Turing complete programming language. Ansible playbooks have variables, loops, conditionals, scoping rules, inheritance, and you can even extend it by writing custom modules in Python, which is a Turing complete language. The problem with not using a real programming language when you're trying to essentially "program" is that you're expressing complex programs without any of the abstractions and tooling support that a real language has. Despite all that I like Ansible's constrained format and the resulting simplicity compared to Chef. But I think we can take those design aesthetics and apply it in a statically typed library and maybe get something more sturdy.

crdoconnor 9y ago
>Ansible playbooks have variables, loops, conditionals, scoping rules, inheritance As far as I am aware, variables, scoping rules and inheritance don't imply turing completeness and the way it does loops and conditionals could really more be characterized as configuration for loops/conditionals further down the stack (e.g. as seen here http://docs.ansible.com/ansible/latest/playbooks_loops.html#loops-and-includes-in-2-0 http://docs.ansible.com/ansible/latest/playbooks_loops.html#... ) >you can even extend it by writing custom modules in Python, which is a Turing complete language. Yes, the idea is that you have the power to break into a (good) turing complete language when it is necessary but you can keep that code - and by extension the technical debt it would attract - to an absolute minimum. I've personally never felt the need to write a custom module in python when using ansible despite using it a lot, so for me, minimum is zero. I'm sure I'm not alone either. >The problem with not using a real programming language when you're trying to essentially "program" is that you're expressing complex programs without any of the abstractions and tooling support that a real language has. Yes, this is a problem if you're trying to work within a problem space that is not heavily constrained. If almost every time I used ansible I felt the need to write a python module to do almost everything I would agree that it is a fundamentally unsuitable task. I feel this issue when writing build scripts which I think absolutely have to be kept turing complete, but never server orchestration.
- leg100 9y ago
  > As far as I am aware, variables, scoping rules and inheritance don't imply turing completeness and the way it does loops and conditionals could really more be characterized as configuration for loops/conditionals further down the stack (e.g. as seen here http://docs.ansible.com/ansible/latest/playbooks_loops.html#.. http://docs.ansible.com/ansible/latest/playbooks_loops.html#.... ) Then what does imply turing completeness? According to the wikipedia article [1]: "To show that something is Turing complete, it is enough to show that it can be used to simulate some Turing complete system. For example, an imperative language is Turing complete if it has conditional branching (e.g., "if" and "goto" statements, or a "branch if zero" instruction; see one instruction set computer) and the ability to change an arbitrary amount of memory (e.g., the ability to maintain an arbitrary number of variables). Since this is almost always the case, most if not all imperative languages are Turing complete if the limitations of finite memory are ignored." [1] https://en.wikipedia.org/wiki/Turing_completeness https://en.wikipedia.org/wiki/Turing_completeness
  - deleted 9y ago
    [deleted]
  - crdoconnor 9y ago
    >Then what does imply turing completeness? If it did arbitrary branching and if you could mutate a variable and then reuse it later on in a playbook.
    - Spivak 9y ago
      The branching is a given. Variable mutation is totally possible with set_fact.
jmcnulty 9y ago
> and you can even extend it by writing custom modules in Python Actually you can write custom modules in any language proving when you exit you provide the required JSON to indicate if the module succeeded or failed, changed something, or has a message to pass back.

by jasim 9y ago

crdoconnor 9y ago

>Ansible playbooks have variables, loops, conditionals, scoping rules, inheritance As far as I am aware, variables, scoping rules and inheritance don't imply turing completeness and the way it does loops and conditionals could really more be characterized as configuration for loops/conditionals further down the stack (e.g. as seen here http://docs.ansible.com/ansible/latest/playbooks_loops.html#loops-and-includes-in-2-0 http://docs.ansible.com/ansible/latest/playbooks_loops.html#... ) >you can even extend it by writing custom modules in Python, which is a Turing complete language. Yes, the idea is that you have the power to break into a (good) turing complete language when it is necessary but you can keep that code - and by extension the technical debt it would attract - to an absolute minimum. I've personally never felt the need to write a custom module in python when using ansible despite using it a lot, so for me, minimum is zero. I'm sure I'm not alone either. >The problem with not using a real programming language when you're trying to essentially "program" is that you're expressing complex programs without any of the abstractions and tooling support that a real language has. Yes, this is a problem if you're trying to work within a problem space that is not heavily constrained. If almost every time I used ansible I felt the need to write a python module to do almost everything I would agree that it is a fundamentally unsuitable task. I feel this issue when writing build scripts which I think absolutely have to be kept turing complete, but never server orchestration.

leg100 9y ago
> As far as I am aware, variables, scoping rules and inheritance don't imply turing completeness and the way it does loops and conditionals could really more be characterized as configuration for loops/conditionals further down the stack (e.g. as seen here http://docs.ansible.com/ansible/latest/playbooks_loops.html#.. http://docs.ansible.com/ansible/latest/playbooks_loops.html#.... ) Then what does imply turing completeness? According to the wikipedia article [1]: "To show that something is Turing complete, it is enough to show that it can be used to simulate some Turing complete system. For example, an imperative language is Turing complete if it has conditional branching (e.g., "if" and "goto" statements, or a "branch if zero" instruction; see one instruction set computer) and the ability to change an arbitrary amount of memory (e.g., the ability to maintain an arbitrary number of variables). Since this is almost always the case, most if not all imperative languages are Turing complete if the limitations of finite memory are ignored." [1] https://en.wikipedia.org/wiki/Turing_completeness https://en.wikipedia.org/wiki/Turing_completeness
- deleted 9y ago
  [deleted]
- crdoconnor 9y ago
  >Then what does imply turing completeness? If it did arbitrary branching and if you could mutate a variable and then reuse it later on in a playbook.
  - Spivak 9y ago
    The branching is a given. Variable mutation is totally possible with set_fact.

jmcnulty 9y ago

> and you can even extend it by writing custom modules in Python Actually you can write custom modules in any language proving when you exit you provide the required JSON to indicate if the module succeeded or failed, changed something, or has a message to pass back.