Squeaky Clean

(Character/isDigit \2)
;;=> true

Instructions

In this exercise you will implement a partial set of utility routines to help a developer clean up identifier names.

In the 5 tasks you will gradually build up the routine clean. A valid identifier comprises zero or more letters and underscores.

In all cases the input string is guaranteed to be non-nil. If an empty string is passed to the clean function, an empty string should be returned.

Note that the caller should avoid calling the routine clean with an empty identifier since such identifiers are ineffectual.

1. Replace any spaces encountered with underscores

Implement the clean function to replace any spaces with underscores. This also applies to leading and trailing spaces.

(clean "my   Id")
;;=> "my___Id"

2. Replace control characters with the upper case string "CTRL"

Modify the clean function to replace control characters with the upper case string "CTRL". A character is considered to be an ISO control character if its code is in the range '\u0000' through '\u001F' or in the range '\u007F' through '\u009F'.

(clean "my\u007FId")
;;=> "myCTRLId"

3. Convert kebab-case to camelCase

Modify the clean function to convert kebab-case to camelCase.

(clean "à-ḃç")
;;=> "àḂç"

4. Omit characters that are not letters

Modify the clean function to omit any characters that are not letters. Note: The underscores must be preserved from the previous step.

(clean "1😀2😀3😀")
;; => ""

5. Omit Greek lower case letters

Modify the clean function to omit any Greek letters in the range 'α' to 'ω'.

(clean "MyΟβιεγτFinder")
;;=> "MyΟFinder"