def replace_leading_spaces(text):
    """
    Replaces leading spaces in a string with ' '.

    Args:
        text: The input string.

    Returns:
        The string with leading spaces replaced by ' '.
    """

    leading_spaces = 0
    for char in text:
        if char == " ":
            leading_spaces += 1
        else:
            break

    if leading_spaces > 0:
        return " " * leading_spaces + text[leading_spaces:]
    else:
        return text


# Example usage:
text1 = "   Hello, world!"
text2 = "No leading spaces."
text3 = "      Another example."
text4 = "\t Test with tabs"  # this will not be replaced, only standard spaces

result1 = replace_leading_spaces(text1)
result2 = replace_leading_spaces(text2)
result3 = replace_leading_spaces(text3)
result4 = replace_leading_spaces(text4)

print(f"'{text1}' becomes '{result1}'")
print(f"'{text2}' becomes '{result2}'")
print(f"'{text3}' becomes '{result3}'")
print(f"'{text4}' becomes '{result4}'")