function read(source: string): string {
    return source;
}

function eval_(ast: string): string {
    return ast;
}

function print(form: string): string {
    return form
}

function rep(source: string): string{
    return print(eval_(read( source)))
}

function* readUserInputs(): Generator<string>{
    while(true){
        const u =  prompt("user> ")
        if(u === null){
            return
        }
        yield u
    }
}


function main(): void {
     for(const userInput of readUserInputs()){
         rep(userInput);
     }


}

main();