## Step 1: Define the Electric Vehicle data type

If you are looking for Haskell assignment help, we define a custom data type, ElectricVehicle, which represents essential information about an electric vehicle. This data type will hold values for efficiency (measured in kWh/mile) and battery capacity (measured in kWh).

```haskell

data ElectricVehicle = ElectricVehicle { efficiency :: Double, batteryCapacity :: Double }

```

**Explanation:
**

- We use the data keyword to define a new algebraic data type named ElectricVehicle.
- Inside the data type definition, we have two fields: efficiency and batteryCapacity. Each field is associated with a type, which is Double in this case.

## Step 2: Calculate Energy Demand for a Single Electric Vehicle

Next, we create a function called `energyDemand`, enabling us to calculate the energy demand for charging a single electric vehicle. The function multiplies the vehicle's efficiency, battery capacity, and the number of charging hours to derive the total energy required.

```haskell

energyDemand :: ElectricVehicle -> Double -> Double

energyDemand ev hours = efficiency ev * batteryCapacity ev * hours

```

**Explanation:
**

- The energyDemand function takes two arguments: an ElectricVehicle and the number of charging hours.
- It calculates the energy demand by multiplying the vehicle's efficiency, battery capacity, and charging hours.

## Step 3: Calculate Total Energy Demand for Multiple Electric Vehicles

To cater to scenarios where multiple electric vehicles need to be charged, we introduce the `totalEnergyDemand` function. This function takes a list of `ElectricVehicle`s and the total number of charging hours, summing up the energy demand for all vehicles.

```haskell

totalEnergyDemand :: [ElectricVehicle] -> Double -> Double

totalEnergyDemand evs hours = sum $ map (\ev -> energyDemand ev hours) evs

```

**Explanation:
**

- The totalEnergyDemand function takes a list of ElectricVehicle and the number of charging hours.
- It calculates the energy demand for each electric vehicle using the energyDemand function and then sums up the results using sum.

## Step 4: Putting it All Together in The Main Function

In the final step, we integrate all the pieces into the `main` function. We create instances of electric vehicles with different efficiency and battery capacity values, set the charging hours, calculate the total energy demand, and display the results.

```haskell

main :: IO ()

main = do

let ev1 = ElectricVehicle { efficiency = 0.25, batteryCapacity = 60 }

ev2 = ElectricVehicle { efficiency = 0.20, batteryCapacity = 75 }

ev3 = ElectricVehicle { efficiency = 0.22, batteryCapacity = 70 }

chargingHours = 8

let evs = [ev1, ev2, ev3]

let totalDemand = totalEnergyDemand evs chargingHours

putStrLn $ "Total energy demand for charging all vehicles: " ++ show totalDemand ++ " kWh"

```

**Explanation:
**

- In the main function, we create three instances of electric vehicles ev1, ev2, and ev3 with different efficiency and battery capacity values.
- We set the number of charging hours to 8 using the chargingHours variable.
- We create a list evs containing all three electric vehicles.
- We calculate the total energy demand by calling the totalEnergyDemand function with the list of electric vehicles and the number of charging hours as arguments.
- Finally, we print the total energy demand in kWh to the console using putStrLn.

## Conclusion:

By following this guide, you have learned how to create a Haskell program that efficiently calculates the energy demand for charging electric vehicles, a crucial step towards promoting eco-friendly transportation. Haskell's functional approach, combined with its concise syntax, allows for elegant and effective solutions to complex problems, making it a valuable skill for aspiring programmers. Happy coding, and let's continue to drive innovation towards a greener future!