codemix / babel-plugin-contracts Goto Github PK

Hey there, I'm trying out this lib, and I have the following function:

export const fib = (n) => {
  pre: {
    Number.isInteger(n);
    n > 0;
  }

  if (n === 0) {
    return 1;
  } else {
    return n + fib(n - 1);
  }

  post: {
    Number.isInteger(it);
    it > 0;
  }
};

when I run fib(5) I get Error: Function precondition failed: n > 0

This shouldn't happen right?

Whole testbed is here: https://github.com/sdellysse/contract-test-n-zero

Hello,
Thank you for this DBC library for JS.
I am encountering an issue with Webpack and Babel-loader plugin, where I set options to change the var names (for example "result" instead of "it"), but those are not used, and the default var names are used instead.
I have included a (basic) testcase.
Regards.

testcase-babel-webpack.zip

After some head scratching over an error about length being undefined, I realized you added a body around the pre label and the main label was gone. It might not be a bad idea to add a migration section to your readme about these changes as they don't jump out that it changed.

The error I was getting was the following:

Module build failed: TypeError: /electron/src/main.js: Cannot read property 'length' of undefined
    at LabeledStatement (/electron/node_modules/babel-plugin-contracts/lib/index.js:775:41)

Hello,

I used to use contracts in Racket of all languages, so glad to see something similar exists for JS!

Anyway, every time I try to compile anything with the contracts plugin, I get Unexpected token (2:9). It doesn't matter what is at position 2:9, even comments will trigger the same error.

.babelrc

{
  "plugins": [
    ["contracts", {
      "names": {
        "assert": "assert",
        "precondition": "pre",
        "postcondition": "post",
        "invariant": "invariant",
        "return": "it",
        "old": "old"
      }
    }]
  ]
}

test.js

const add1 = n => {
	pre: typeof n === 'number';
	return n + 1
}

babel --version

6.26.0 (babel-core 6.26.3)

Do I need babel 7 for this? 6.26.3 is the latest version in npm.

https://www.npmjs.com/package/babel-core

Post-conditions introduce a special variable, it which refers to the result of the function.

Could you add a property—like env—that would let us use a custom variable name of our choosing?
cf

e.g.

{
  "pre": ""
  "post": ""
  "invariant": "",
  "it": ""
}

Is this plugin compatible with babel 7?

relevant excerpt of the stack strace:

…node_modules/babel-plugin-contracts/lib/index.js:37:15
…node_modules/@babel/template/lib/populate.js:35:15

First, thanks so much for a fantastic library!

I was an Eiffel programmer once upon a time and miss DbC. Babel Contracts is the closest I've seen to Eiffel's implementation, and the smoothest. I have already started adding contracts to my code.

Two additions to the library would be most welcome:

• Class invariants
• rescue (as Eiffel would call it)

For the former, imagine this: We place an invariant structure on the constructor of a class, and that invariant is then automatically applied to the beginning and end of each method call (although I admit that I'm not sure what to do about getters and setters). The invariant would not be applied to the constructor, of course, as the instance is still developing.

As for the latter, a rescue clause would allow us to do the following:

• Restore the method to a stable state
• Intercept the exception Contracts throws when the contract is violated, and then re-throw it, most likely with a new Error (and the violation as an inner error)
• Introduce a violation() method for capturing the contract exception thrown by Contracts

Consider the following trivial example:

setStatus(status) {
   require: {
      status;
      typeof status === 'string';
   }

   this.status = status;

   ensure: {
      this.status === 'status';
   }

   rescue: {
      throw new Error('Status was not set', violation());
   }
}

Do you think these things are doable?

Thank you!