An attempt to solve the Mars Rover Kata (https://codurance.com/2017/11/16/katas-for-functional-calisthenics/#marsroverkata), assuming an unlimited world and without wrapping. Try it in the Ramda REPL (https://ramdajs.com/repl/).

rover.js

const moveRover = curry((initialPosition, commands) => {
  return commands.reduce(moveRoverOnce, initialPosition);
});

const moveRoverOnce = (position, command) => pipe(
  mapToInternalFormat,
  rotate(command),
  move(command),
  mapBack
)(position);

const mapToInternalFormat = position => ({
  x: position.x,
  y: position.y,
  angle: getAngleFromOrientation(position.orientation)
});

const getAngleFromOrientation = (orientation) => ({
  'W': 0,
  'N': Math.PI / 2,
  'E': Math.PI,
  'S': Math.PI * 1.5
})[orientation];

const rotate = curry((command, internalPosition) => ({
  ...internalPosition,
  angle: internalPosition.angle += getAngleFromDirection(command)
}));

const getAngleFromDirection = (direction) => ({
  l: -Math.PI / 2,
  r: Math.PI / 2,
  f: 0,
  b: 0
})[direction];

const move = curry((command, position) => ({
  ...position,
  x: position.x + Math.cos(position.angle) * getSpeed(command),
  y: position.y + Math.sin(position.angle) * getSpeed(command)
}));

const getSpeed = (command) => ({
  l: 0,
  r: 0,
  f: 1,
  b: -1
})[command];

const mapBack = internalPosition => ({
  x: internalPosition.x,
  y: internalPosition.y,
  orientation: getOrientationFromAngle(Math.round(internalPosition.angle / Math.PI * 180))
});
                                     
const getOrientationFromAngle = (angle) => ({
  0: 'E',
  90: 'N',
  180: 'W',
  270: 'S'
})[angle];

const initialPosition = {
  x: 10,
  y: 3,
  orientation: 'N'
};

const commands = ['f', 'f', 'b', 'l', 'f', 'r', 'r', 'f'];

const expectedEndPosition = {
  x: 10,
  y: 4,
  orientation: 'E'
};

const moveRoverFromInitialPosition = moveRover(initialPosition);
const actualEndPosition = moveRoverFromInitialPosition(commands);

equals(actualEndPosition, expectedEndPosition);