Scalar

Returns a function that takes an optional arg and uses it as the operand or injects a argument from some other source (e.g., HTML element, query string).

When called, the returned function returns the operand if it matches the type, otherwise returns an Error.

• IsBoolean = operand => (arg => Either<Error, Boolean)
• IsNumber = operand => (arg => Either<Error, Number)
• IsString = operand => (arg => Either<Error, String)