nth-check

Returns a function that checks if an elements index matches the given rule highly optimized to return the fastest solution.

Parameter parsed

A tuple [a, b], as returned by parse.

Returns

A highly optimized function that returns whether an index matches the nth-check.

Example 1

const check = nthCheck.compile([2, 3]);

check(0); // `false`
check(1); // `false`
check(2); // `true`
check(3); // `false`
check(4); // `true`
check(5); // `false`
check(6); // `true`

Returns a function that produces a monotonously increasing sequence of indices.

If the sequence has an end, the returned function will return null after the last index in the sequence.

Parameter parsed

A tuple [a, b], as returned by parse.

Returns

A function that produces a sequence of indices.

Example 1

Always increasing (2n+3)

const gen = nthCheck.generate([2, 3])

gen() // `1`
gen() // `3`
gen() // `5`
gen() // `8`
gen() // `11`

Example 2

With end value (-2n+10)

const gen = nthCheck.generate([-2, 5]);

gen() // 0
gen() // 2
gen() // 4
gen() // null

Parses and compiles a formula to a highly optimized function. Combination of parse and compile.

If the formula doesn't match any elements, it returns [boolbase](https://github.com/fb55/boolbase)'s falseFunc. Otherwise, a function accepting an _index_ is returned, which returns whether or not the passed _index_ matches the formula.

Note: The nth-rule starts counting at 1, the returned function at 0.

Parameter formula

The formula to compile.

Example 1

const check = nthCheck("2n+3");

check(0); // false check(1); // false check(2); // true check(3); // false check(4); // true check(5); // false check(6); // true

Parses an expression.

Returns

An array containing the integer step size and the integer offset of the nth rule.

Throws

An Error if parsing fails.

Example 1

nthCheck.parse("2n+3"); // returns [2, 3]

Parses and compiles a formula to a generator that produces a sequence of indices. Combination of parse and generate.

Parameter formula

The formula to compile.

Returns

A function that produces a sequence of indices.

Example 1

Always increasing

const gen = nthCheck.sequence('2n+3')

gen() // `1`
gen() // `3`
gen() // `5`
gen() // `8`
gen() // `11`

Example 2

With end value

const gen = nthCheck.sequence('-2n+5');

gen() // 0
gen() // 2
gen() // 4
gen() // null