xodio / eslint-plugin-xod-fp

Limit the chaos while doing FP in JS

eslint-plugin-xod-fp

ESLint plugins to check code written in functional style with Ramda.

Installation

You'll first need to install ESLint:

$ npm i eslint --save-dev

Next, install eslint-plugin-xod-fp:

$ npm install eslint-plugin-xod-fp --save-dev

Note: If you installed ESLint globally (using the -g flag) then you must also install eslint-plugin-xod-fp globally.

Usage

Add xod-ramda to the plugins section of your .eslintrc configuration file. You can omit the eslint-plugin- prefix:

{
  "plugins": [
    "xod-fp"
  ]
}

Then configure the rules you want to use under the rules section.

{
  "rules": {
    "xod-fp/max-composition-depth": [ "error", 5 ],
  }
}

Supported Rules

• max-composition-depth: limit compositional calls nesting

Rule: max-composition-depth

Ensure that function compositions are not too deep.

Valid

// :: Node -> Boolean
const isCallExpression = R.propEq('type', 'CallExpression');

// :: Node -> Boolean
const isArrowFunctionExpression = R.propEq('type', 'ArrowFunctionExpression');

// :: Node -> Boolean
const isCurry = R.allPass([
  R.propEq('type', 'CallExpression'),
  R.pathEq(['callee', 'type'], 'MemberExpression'),
  R.pathEq(['callee', 'object', 'type'], 'Identifier'),
  R.pathEq(['callee', 'object', 'name'], 'R'),
  R.pathEq(['callee', 'property', 'type'], 'Identifier'),
  R.pathEq(['callee', 'property', 'name'], 'curry'),
]);

// :: Node -> Boolean
const isCallNotCurry = R.both(
  isCallExpression,
  R.complement(isCurry)
);

// :: Options -> Node -> Boolean
const isNestingExpression = opts => R.anyPass([
  opts.ignoreCurry ? isCallNotCurry : isCallExpression,
  opts.ignoreArrow ? R.F : isArrowFunctionExpression,
]);

// :: Node -> [Node] -- a chain of parents to the root
const parents = R.ifElse(
  R.prop('parent'),
  R.compose(parent => R.concat([parent], parents(parent)), R.prop('parent')),
  R.always([])
);

// :: Options -> Node -> Number
const nestingDepth = R.curry((opts, node) => R.compose(
  R.length,
  R.uniq,
  R.map(R.prop('start')),
  R.filter(isNestingExpression(opts)),
  parents
)(node));

Invalid

// :: Options -> Node -> Number
// -- No R.compose (depth is 7)
const nestingDepth = R.curry((opts, node) =>
  R.length(R.uniq(R.map(
    R.prop('start'), R.filter(isNestingExpression(opts)), parents(node)
  )))
);

// :: Options -> Node -> Number
// -- Too complex inlining (depth is 8)
const nestingDepth = R.curry((opts, node) => R.compose(
  R.length,
  R.uniq,
  R.map(R.prop('start')),
  R.filter(opts => R.anyPass([
      opts.ignoreCurry ? R.allPass([
        R.propEq('type', 'CallExpression'),
        R.pathEq(['callee', 'type'], 'MemberExpression'),
        R.pathEq(['callee', 'object', 'type'], 'Identifier'),
        R.pathEq(['callee', 'object', 'name'], 'R'),
        R.pathEq(['callee', 'property', 'type'], 'Identifier'),
        R.pathEq(['callee', 'property', 'name'], 'curry'),
      ]) : R.propEq('type', 'CallExpression'),
      opts.ignoreArrow ? R.F : R.propEq('type', 'ArrowFunctionExpression'),
  ])),
  R.ifElse(
    R.prop('parent'),
    R.compose(parent => R.concat([parent], parents(parent)), R.prop('parent')),
    R.always([])
  )
)(node));

Options

max

Defaults to 4.

Maximal nesting depth. Nested function call or arrow function expression increment the depth.

ignoreArrow

Defaults to false.

Pass { ignoreArrow: true } to not to take arrow functions into account when counting the depth.

ignoreCurry

Defaults to false.

Pass { ignoreCurry: true } to not to take R.curry calls into account when counting the depth.

Calling R.curry is just a fighting with JavaScript to make it more FP-compatible. If you see R.curry you probably would not think about it at all trying to understand what an overall function does. So it is a good idea to ignore currying in depth calculation as well.

ignoreMocha

Defaults to false.

Pass { ignoreMocha: true } to not to take it and describe calls of Mocha into account when counting the depth. Child arrow functions of it and describe will be ignored as well.

Mocha’s functions are part of testing DSL and are not part of functions logic, so do not add to a function complexity thus can be ignored.