Replacing all occurrences in a String
Your desire to use the "functional way" is not well-motivated. Why do it "the functional way" when the "other way" is not only easier to read, but also common practice, and well-understood?

val stripCurly = "[{}]".r

val replaced = stripCurly.replaceAllIn(a, "")


If you want to have forced-matching of the braces consider:

val pure = """\{([^}]*)\}""".r
val pured = pure.replaceAllIn(content, "$1")


Note the use of the "not a } inside the {}" logic in the regex.

The examples above are running here in ideone