Sign

Sign is a curried constructor used to create a JS/JSON configuration object that represents a sign operation.

const Sign =
  (datatype = "Number") =>
  operand => ({
    tag: "Sign",
    operand,
    datatype,
  })
 
export default Sign
 

The first parameter to Sign determines the datatype of the return value of the sign operation: Number (float) or Integer.

The second parameter is an operation that must eventually evaluate to a numerical value. This is the operand for which we will calculate the sign.

The operand operation (add, subtract, etc.) may include nested operations to any depth, but the bottom (leaf) nodes must return values. Values are injected with injectors.

Because Sign is curried, we can simplify our code by partial application, for example, const S = Sign("Integer"). This returns a function that takes the operand operation and returns an Sign configuration object for working with integers.

See below for an example.

The sign function

We pass our configuration object to composeOperators, which composes the operations and returns a single function. This function takes an optional argument and returns the result of the calculation as a Right, e.g., { right: 42 }, or a Left with an array of Error objects, { left: [Error] }.

const sign = operation => (arg? => Either<Array<Error>, result>)

composeOperators works by recursing down through the operation object, calling the correct operator function based on the tag (e.g., "Sign"), and composing the functions returned. composeOperators then returns this composed function. See composeOperators for a more detailed explanation.

The injectors are not called until this composed calculate function is run. Hence, evaluation is lazy: the values are not injected until the last moment.

See the injectors for a complete list of how values may be injected. See the list of operators for the full range of available mathematical operations.

Example

We use composeOperators to create a calculate function, passing it our Sign operation object. We call the calculate function and pass it an (optional) argument to run our operation(s) and calculate the product.

Here our operation includes an operand in which the value is passed in via the optional argument to calculate. This is done using FromArgument.

Try leaving one of the numbers undefined to see an Error returned.