$E_i=T|T+E|$

$T$:$=N|N**T|$

$N$:$=D|-D|$

$D$:$=0|1|2|3|4|5|6|7|8|9|$

Where $E,T,N$ and $D$ are non$-$terminals, and $E$ is the start symbol. The $+,{?}^{**}--,0,1,2,3,4,5,6,7,8,9$ are the terminals. The $"||"$ used in the grammar is neither terminal or non$-$terminal, simply interpret it as $"$or$"$ in English.

Implement a front$-$end recursive$-$descent parser in Golang language that accepts strings from standard input $($one per line$)$ until EOF and determines whether each string is in the language defined by this grammar. First, develop a Scanner part into your program that leaves out the whitespace$($s$)$ of the input string and creates a list of lexical units to be parsed. Your program then should validate if each of the lexical units are lexemes $($valid lexical units$)$ according to the grammar $($Section $2).$

Hints: In Golang, the Fields $0$ function associated with string breaks a string around each instance of one or more consecutive white space characters into an Array. For example, myArray:$=$ strings: Fields$($myEtring$)$ splits mystring into characters separated by whitespace$($s$).$ Java, you may have used mystring.trimo solit $("$s$+")$ where $"s{t}^{\text{'}}$ represents the regular expression for one or more whitespace, tab, etc characters.