Implement cond

[leonid-shutov]

#9

• tests and linter show no problems (npm t)
• tests are added/updated for bug fixes and new features
• code is properly formatted (npm run fix)
• description of changes is added in CHANGELOG.md
• update .d.ts typings

[leonid-shutov]

avoid creating an extra array as Murych suggested

[leonid-shutov]

I think information expert works well here

[tshemsedinov]

• Compact empty lines and one-operator blocks
• Move oll fields to constructor

[tshemsedinov]

I do not understood moving from Array.from to for..of solution, please explain.

Suggested change

	let header = '(';
	for (const identifier of this.identifiers) {
	if (header.length > 1) header += ', ';
	header += identifier;
	}
	header += ')';
	return `${header} => ${this.toExpression()}`;
	}
	let header = '';
	for (const identifier of this.identifiers) {
	if (header) header += ', ';
	header += identifier;
	}
	return `(${header}) => ${this.toExpression()}`;
	}

[leonid-shutov]

Murych suggested to avoid creating an extra array. Just not sure if concatenating strings is as fast as Array.join

[tshemsedinov]

• I do not like disabled eslint rules, just make return consistent.
• !== false is not ok, see fix
• It is not ok to start reducing from undefined in most cases, it is also strange to use reduce with ignored accumulator arg

Suggested change

	// eslint-disable-next-line consistent-return
	interpret(context) {
	for (const { condition, consequents } of this.clauses) {
	if (condition.interpret(context) !== false) {
	return consequents.reduce(
	(_, consequent) => consequent.interpret(context),
	undefined,
	);
	}
	}
	}
	interpret(context) {
	for (const { condition, consequents } of this.clauses) {
	if (condition.interpret(context)) {
	return consequents.reduce(
	(_, consequent) => consequent.interpret(context),
	undefined,
	);
	}
	}
	}

[leonid-shutov]

We can't do if(condition.interpret(context)) because in LISP condition is false only if it evaluates to nil while in JavaScript it can be any falsy value like 0. E.g. (cond (0 x)) would be a true condition.

This is why I did !== false (nil is interpreted to false in our current solution). I've made this explicit in the latest commit.

[tshemsedinov]

Suggested change

	const consequentExpressions = consequents.map((consequent, i) =>
	i === consequents.length - 1
	? `return ${consequent.toExpression()};`
	: `${consequent.toExpression()};`,
	);
	const consequentExpressions = consequents.map((consequent, i) => {
	const ex = consequent.toExpression();
	return i === consequents.length - 1 ? `return ${ex};` : `${ex};`;
	});

[tshemsedinov]

We have head and tail utilities

[tshemsedinov]

We need to see you on the call one time