Clojure symbol regex

README.md

Blog 2019/9/1

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Clojure symbol regex

Trying to work out what patterns would be used for a regex-based lexer for clojure.

It appears to work: https://regex101.com/r/Qs0gLH/4

Note: this doesn't include recognizing keywords.

see also:

• https://github.com/edn-format/edn
• https://clojure.org/reference/reader
• https://github.com/clojure/clojure/blob/c6756a8bab137128c8119add29a25b0a88509900/src/jvm/clojure/lang/EdnReader.java#L27

output.txt

$ ./symbol-regex.py 
([a-zA-Z\.\*+!\-_?$%&=<>][a-zA-Z0-9\.\*+!\-_?$%&=<>]+\/[a-zA-Z\.\*+!\-_?$%&=<>][a-zA-Z0-9\.\*+!\-_?$%&=<>]+)|([a-zA-Z\.\*+!\-_?$%&=<>][a-zA-Z0-9\.\*+!\-_?$%&=<>]+\/[a-zA-Z\.\*+!\-_?$%&=<>\/])|([a-zA-Z\.\*+!\-_?$%&=<>]\/[a-zA-Z\.\*+!\-_?$%&=<>][a-zA-Z0-9\.\*+!\-_?$%&=<>]+)|([a-zA-Z\.\*+!\-_?$%&=<>]\/[a-zA-Z\.\*+!\-_?$%&=<>\/])|([a-zA-Z\.\*+!\-_?$%&=<>][a-zA-Z0-9\.\*+!\-_?$%&=<>]+)|([a-zA-Z\.\*+!\-_?$%&=<>\/])

symbol-regex.py

#!/usr/bin/env python

# a program to generate the regex for a symbol in clojure.

"""
character classes:
- `a` (alpha): `[a-zA-Z]`
- `n` (num): `[0-9]`
- `s` special: `[\.\*+!\-_?$%&=<>]`
- `l` slash: `\/`
- `c` colon: `:`

a symbol can be:
- multi-char prefix, multi-char name: `[as][ans]+l[as][ans]+`
- multi-char prefix, single-char name: `[as][ans]+l[asl]`
- single-char prefix, multi-char name: `[as]l[as][ans]+`
- single-char prefix, single-char name: `[as]l[asl]`
- multi-char name: `[as][ans]+`
- single-char name: `[asl]`
"""

import sys

# character classes:
a = "a-zA-Z"
n = "0-9"
s = "\.\*+!\-_?$%&=<>"
l = "\/"

# a symbol can be:
sys.stdout.write("(")

# a multi-character prefix, multi-character name: `[as][ans]+l[as][ans]+`
sys.stdout.write("[%s%s][%s%s%s]+%s[%s%s][%s%s%s]+" % (a,s, a,n,s, l, a,s, a,n,s))

# or
sys.stdout.write(")|(")

# a multi-character prefix, single-character name: `[as][ans]+l[asl]`
sys.stdout.write("[%s%s][%s%s%s]+%s[%s%s%s]" % (a,s, a,n,s, l, a,s,l))

# or
sys.stdout.write(")|(")

# a single-character prefix, multi-character name: `[as]l[as][ans]+`
sys.stdout.write("[%s%s]%s[%s%s][%s%s%s]+" % (a,s, l, a,s, a,n,s))

# or
sys.stdout.write(")|(")

# a single-character prefix, single-character name: `[as]l[asl]`
sys.stdout.write("[%s%s]%s[%s%s%s]" % (a,s, l, a,s,l))

# or
sys.stdout.write(")|(")

# a multi-character name: `[as][ans]+`
sys.stdout.write("[%s%s][%s%s%s]+" % (a,s, a,n,s))

# or
sys.stdout.write(")|(")

# a single-character name: `[asl]`
sys.stdout.write("[%s%s%s]" % (a, s, l))

sys.stdout.write(")\n")