Eval

Implement a web service that will evaluate simple math word problems, with the following endpoints:

POST /evaluate

• Parse and evaluate a problem expression returning the answer as an integer.
• Expressions with no operations simply evaluate to the number given:
  • "What is 5?" should return 5.
• Simple arithmetic:
  • Add two numbers together
    • What is 5 plus 13?
  • Subtraction
    • What is 7 minus 5?
  • Multiplication
    • What is 6 multiplied by 4?
  • Division
    • What is 25 divided by 5?
• Handle a set of operations, in sequence.
  • Since these are verbal word problems, evaluate the expression from left-to-right, ignoring the typical order of operations.
  • What is 3 plus 2 multiplied by 3? 15 (i.e. not 9)
• The service should return error on:
  • Unsupported operations ("What is 52 cubed?")
  • Non-math questions ("Who is the President of the United States?")
  • Expressions with invalid syntax ("What is 1 plus plus 2?")
• The endpoint should accept json data in the following format: {"expression":"<a simple math problem>"}
• The endpoint should return json data in the following format: {"result":<the expression's result>}

POST /validate

• Validate an expression, return if valid or not.
• The endpoint should accept json data in the following format: {"expression":"<a simple math problem>"}
• The endpoint should return json data in the following format:
  • If the expression is not valid:

      {
          "valid":false,
          "reason":"<the reason why the expression is invalid>"
      }
  

  • If the expression is valid: {"valid":true}

GET /errors

• Return all errors occurred with their frequency (e.g. if the same unsupported expression is submitted many times), URL of the endpoint on which they have occurred (i.e. /evaluate or /validate) and the type of the error (e.g. Unsupported operations).
• The endpoint should return json data in the following format:

[
    {
        "expression": "<a simple math problem>",
        "endpoint": "<endpoint URL>",
        "frequency": <number of times the expression failed>,
        "type": "<error type>"
    }
]

Please note that for the purpose of the task it is fine for the web service to persist all data in memory.

(OPTIONAL):

• Implement CLI client that will provide the same set of functionality and will use the web service as its backend.