Why to write this engine？

Because I coded a super calculator last year which is in Appstore， the super calculator is based on one more completed parser.

This parser is just a simplified prototype. It calculates more than fraction, normal expression as well, so you can expand this library to normal calculation，detail illustration will be added in the near future.

Parser Theory : Gradient descent

Parser Process:

For example：1+2*（3-4） parsing process：

1. Tokenizer: Tokens：1, +, 2, *, (, 3, -, 4, ）

2. Interpreter： Indicate the vague tokens，such as '+' means add or positive ，so is 'negative'.

3. Parser

AST(抽象树)：

In fact, the math expression is parsed into one custom nested cluster in code，and then resolve each level group sub expression from inside to outside.

Tips：

1. adjust number ,which is regarded as fraction through process，such as

   2 convert to 2/1 ; 0.2 convert to 2/10; 0.9998 convert to 9998/10000

2. because of object-c without function operator,we need convert operators,such as @"+", to function name,such as "add"

Todo ：

1 processing，

2 demo，

3 more test