Add `to-ascii` function

[obycode]

It may prove useful to add a generic to-string function that can take any value and return a string representation of it.

[jbencin]

Specifically, this came up in a conversation about converting principal types to strings. This is absolutely necessary for cross-chain messaging, but Clarity has no built-in function for it

The the only way I've seen to do this so far (see here) is rather ugly

[obycode]

I guess this should actually be to-ascii and to-utf8.

[obycode]

Proposal for Clarity 4: implement to-ascii with support for a subset of Clarity types as inputs, specifically:

• int
• uint
• bool
• principal
• buff
  • Will fail if the buff is longer than 1048574, since the string needs two characters for the 0x
• string-utf8
  • Will fail if the string contains non-ascii characters

This intentionally excludes complex types to avoid the extra complexity initially:

• list
• tuple
• optional
• response

Support for these complex types could be added in a future version of Clarity.

[obycode]

Latest design

to-ascii is a new Clarity function that converts simple values into their
string-ascii representations.

• Input: int | uint | bool | principal | (buff 524284) |
  (string-utf8 1048571)
• Output: (response (string-ascii 1048571) uint)
• Signature: (to-ascii value)
• Description: Returns the string-ascii representation of the input value
  in an ok response on success. The only error condition is if the input type
  is string-utf8 and the value contains non-ASCII characters, in which case,
  (err u1) is returned.
• Example:

  (to-ascii true) ;; Returns (ok "true")
  (to-ascii 42) ;; Returns (ok "42")
  (to-ascii 'SP2QEZ06AGJ3RKJPBV14SY1V5BBFNAW33D96YPGZF) ;; Returns (ok "SP2QEZ06AGJ3RKJPBV14SY1V5BBFNAW33D96YPGZF")
  (to-ascii 0x12345678) ;; Returns (ok "0x12345678")

[obycode]

Added in Clarity 4, to be activated with Epoch 3.3 (pending successful vote).