Pythonic String Reader

This is a piece of code stolen from Yury Sulsky which has been slightly modified/improved by myself. It sets up some reader macros that make it simpler to input string literals which contain backslashes and double quotes. This is very useful for writing complicated docstrings and, as it turns out, writing code that contains string literals that contain code themselves.

Enabling the syntax

Pythonic String Reader is implemented using modern read-table management libraries like Named Readtables, so it should be even more unintrusive than it was originally designed.

To use the this read macro, you can simply use the readtable pythonic-string-syntax in the package by putting the following at the beginning of your files:

(in-readtable pythonic-string-syntax)

Or use any of the ways Named Readtables allows you to define and combine readtables, for instance:

(defreadtable my-readtable
  (:merge :standard)
  (:merge pythonic-string-syntax))

... or ...

(defreadtable my-readtable
  (:merge :standard)
  (:macro-char #\" #'pythonic-string-reader::read-multiline-string t))

(in-readtable my-readtable)

I don't want to use Named Readtables

To enable the reader syntax, run enable-pythonic-string-syntax and to disable use disable-pythonic-string-syntax.


The string reader will treat any bit of code that contains three consecutive double quotes specially. If it finds three consecutive double quotes, it will start reading and won't stop until it finds another three consecutive double quotes. All text in between is taken as literal. It is impossible to escape anything.

As an extension, if the reader finds four consecutive double quotes (i.e. it finds the opening three double quotes, then finds one more immediately after those), it will do the same as above, except it will not end until it reaches another four consecutive double quotes. This is particularly useful if you want to trick your text editor into treating the string you are writing as normal code instead of a string.


Note that in these examples I still balance quotes. This is needed so that Slime doesn't get confused and think there is still input to be had. This is not the case when code is loaded or compiled using the load or compile-file commands (which is what users will experience).

CL-USER> """ hello\ """
" hello\\ "
CL-USER> """ hello\ """" "
" "
CL-USER> """hello"""
CL-USER> """ \ """
" \\ "
CL-USER> """ " " """
" \" \" "
CL-USER> """" hello """"
" hello "
CL-USER> """" hello """ " """"
" hello \"\"\" \" "


Perhaps I will integrate with CL-Syntactic-Sugar in the future, as that used to be a way to wrangle all of these reader macros in a sane way. I feel like Named-Readtables has accomplished this in a cleaner way though.

Yury Sulsky and Zach Kost-Smith
Zach Kost-Smith <>