Calculator - Discussion

[nyx-4]

Recapitulation of Calculator

The project is proposed in Issue #1. The further discussion on how to implement it will be done here. In the face of ambiguity, refuse the temptation to guess. And just ask.

[kr8457]

hi

[nyx-4]

Make sure to read the fish-shell's math documentation and the these five pages of Dragon Book.

[kr8457]

i have read these

[nyx-4]

@kr8457 As is explained in those five pages of Dragon Book, there will be three parts (or layers) in our project namely Lexical Analyzer, Syntax Analyzer and Calculator. The brief overview is given below, your task is to make a Syntax Analyzer.

Lexical Analyzer #5

Lexical Analyzer is proposed above, it will be made by me.

Syntax Analyzer

The token stream from lexical analyzer is passed as argument to Syntax analyzer, that converts a flat list to tree-like structure in accordance with operator-precedence (which is also passed in as dict, see Operator precedent). The analyzer should convert the list in binary tree-like structure (use your best intuition), it should not solve them.

Operator precedent

Why not support custom operators/symbols? We can use a dict like this, and assume that whatever comes first in operators has higher precedent. I think this may work, but look for edge cases. I am very suspicious of % and /.

operators: dict = {
    "^": lambda x, y: x ** y,
    "%": lambda x, y: x % y,
    "/": lambda x, y: x / y,
    "*": lambda x, y: x * y,
    "-": lambda x, y: x - y,
    "+": lambda x, y: x + y,
}

Tip

Changed in version 3.7: Dictionary order is guaranteed to be insertion order. This behavior was an implementation detail of CPython from 3.6.

Calculator

The last layer will take the binary tree-like structure from Syntax analyzer and calculate the result by passing the arguments in the Callable. It should also handle Exceptions from those Callables. This layer will be simple, because all hard work will already be done by previous two layers.