How to use the command 'eva' (with examples)

The eva command is a simple yet powerful calculator REPL (Read-Eval-Print Loop) that functions similarly to the classic bc command-line calculator. Designed with simplicity and efficiency in mind, eva offers syntax highlighting and persistent history, making it easier for users to input, evaluate, and recall mathematical expressions. Whether used for basic calculations or complex mathematical functions, eva provides a user-friendly interface for quick and accurate computations. More information can be found at eva’s GitHub page .

Use case 1: Run the calculator in interactive mode

Code:

eva

Motivation: Interactive mode is useful when you need to perform a series of calculations without restarting the command or retyping previously entered expressions. This mode enables fluid, ongoing calculations, saving time and effort for users who need to compute multiple expressions in succession.

Explanation: In this scenario, invoking eva without additional arguments starts the calculator in interactive mode. This allows users to input expressions on-the-fly and receive immediate feedback on their mathematical operations.

Example Output: Once you enter eva in the terminal, you are prompted to input expressions directly. The interaction may look like this:

> 2 + 2
4
> 3 * (7 - 2)
15
> quit

Use case 2: Calculate the result of an expression

Code:

eva "(1 + 2) * 2 ^ 2"

Motivation: This use case showcases how eva can be employed for straightforward calculation tasks directly through a command-line argument. It is particularly beneficial when you have a single expression that you want to calculate quickly without entering the interactive mode.

Explanation: The command eva "(1 + 2) * 2 ^ 2" computes the result of a single mathematical expression. The parentheses (1 + 2) denote that addition should occur first, yielding 3. Then, the expression 2 ^ 2 calculates the square of 2, which is 4. Finally, 3 * 4 is evaluated to produce the result.

Example Output: When you run this command, you receive an immediate response displaying the result:

12

Use case 3: Calculate an expression forcing the number of decimal places to 5

Code:

eva --fix 5 "5 / 3"

Motivation: Ensuring precision to a specific number of decimal places is crucial in disciplines like finance or engineering, where rounding inconsistencies can cause significant impacts. This use case demonstrates how users can enforce consistency in numerical output using eva.

Explanation: The flag --fix 5 tells eva to format the result to exactly five decimal places. This is particularly useful for guaranteeing precision across calculations, ensuring that all results adhere to a predetermined level of detail. The interpretable expression 5 / 3 divides 5 by 3, producing the non-terminating decimal 1.66666 with the required precision.

Example Output: The output is formatted to five decimal places as follows:

1.66667

Use case 4: Calculate an expression with sine and cosine

Code:

eva "sin(1) + cos(1)"

Motivation: For users involved in fields such as physics, engineering, or any domain involving trigonometry, calculating expressions that include trigonometric functions like sine and cosine is a common necessity. This example illustrates how eva can handle such calculations efficiently.

Explanation: The expression "sin(1) + cos(1)" uses the sine and cosine functions. These standard trigonometric functions can be computed directly in eva using radian values as input. The command evaluates the sine and cosine of 1 radian and returns the sum of these values.

Example Output: Upon execution, the result is displayed as:

1.38177

Conclusion:

The eva command serves as a versatile tool for performing various mathematical calculations in an accessible, efficient manner. From simple arithmetic to more complex trigonometric expressions, eva handles diverse computational needs with ease. By offering syntax highlighting, persistent history, and flexibility in formatting, it stands as a valuable resource for users seeking precision and convenience in their command-line calculations.