检查SML中的字符串是否包含Pascal整数

open String;

fun isPascalInteger(str: string): bool =
    let
        val len = size str
        fun isDigit(c: char): bool = Char.isDigit c
        fun isSign(c: char): bool = (c = #"+" orelse c = #"-")
        fun isInteger(sub: string): bool =
            let
                val subLen = size sub
            in
                if subLen = 0 then false
                else if subLen = 1 then isDigit(sub)
                else if isSign(sub) then isDigit(sub, 1)
                else isDigit(sub, 0)
            end
    in
        if len = 0 then false
        else
            let
                val regex = "\\b[-+]?\\d+\\b"
                val matches = Str.regMatches (Str.regExp regex) str
                val numMatches = length matches
            in
                if numMatches = 0 then false
                else
                    let
                        val allMatchesAreIntegers = List.all isInteger matches
                    in
                        allMatchesAreIntegers
                    end
            end
    end;