Extended MATH dialect.

math.red

Red [
    Title:  "Extended MATH dialect"
    Author: 9214
    Date:   12-Nov-18
]

math: function [
    "Evaluate expression using PEMDAS precedence rules"
    body [any-list!]
    /local match
][
    table: [
        '**
        ['* | '/ | '% | '//]
        ['+ | '-]
    ]
    
    wrap: [change copy match [skip operator skip] (do match)]
    body: copy/deep body
    
    do also body foreach operator table [
        parse body rule: [
            any [
                if (operator = '**) skip operator rule [fail] 
                | ahead paren! into rule [fail]
                | some [ahead wrap] [fail]
                | skip
            ]
        ]
    ]
]