The goal is to write a program that encodes an other program (input) with the fewest character possible.

###Scoring

• The score is equal to the different number of characters needed for the output.
• Lower score is better.

###Rules

• No target languages with a limited set of commands. (No Brainf**k, Whitespace etc)
  Edit: I mean at least 26 significant characters, A doesn't change the way a brainf**k program operates, so you can't count this character. Same applies to whitespace.
• The target language must exist at the time where this question is written.
• You have to include a small explanation how you archive your score.
• The input program is valid.
• The encoded program must be a valid program in the same language as the input.
• The encoded program must do the same job as the original program.
• Your encoder must work for every valid program in that language.
• Include some sample input and output.

Notes

• The encoder might be written in any language, not only in the language it targets.
• This is not code-golf, readable programs are encouraged.
• The great goal is to see how many different characters are needed to write anything in that language. I disallowed BF etc because there would be no challenge.
• This was inspired by Print a string in as few distinct characters as possible, you could take it as metagolf for that question.

###Example

In Java, you can use \uXXXX instead other characters. A valid entry encodes every character from the input this way. This would have a score of 18. (\ 0-9a-f)

Code in Tcl, encodes a Java program:

set res {}
foreach char [split [read stdin] {}] {
    append res [format \\u%04x [scan $char %c]]
}
puts $res