Curry Calculator

index.js

// https://repl.it/Ccki/2

function calculator(num) {
  var equation = [];

  function captureNumber (num) {
    equation.push(num);
    return captureOperator;
  }

  function captureOperator(op) {

    if (op === '=') {
      return processEquation(equation);
    }

    equation.push(op);
    return captureNumber;
  }

  function processEquation(eqArr) {
    var lastNumSeen = null;
    var lastOpSeen = null;

    return eqArr.reduce(function(sum, curr, index){
      
      if (!index) return sum + curr;

      if (typeof(curr) === 'number') {
        
        switch(lastOpSeen) {
          case '+': return sum + curr;
          case '-': return sum - curr;
          default: console.log('defaulted', curr);
        }
        
        lastOpSeen = null;
        return sum;
      }

      if (typeof(curr) === 'string') {
        lastOpSeen = curr;
        return sum;
      }
    }, 0);
  }
  
  return captureNumber(num);
}

// code commented out is equivalent to line 59
// var getNextOp = calculator(1);
// var getNextNum = getNextOp('+');
// getNextOp = getNextNum(1);
// getNextNum = getNextOp('-');
// getNextOp = getNextNum(1);
// getNextNum = getNextOp('+');
// getNextOp = getNextNum(10);
// var result = getNextOp('=');

var result = calculator(5)('+')(1)('-')(1)('+')(10)('=');
console.log(result);