Evaluating simple Lisp like S-expressions

Python Help
1

I’m looking for the library which can evaluate simple Lisp like S-expressions. Specifically, I have simple function definitions produced by solvers like cvc5, e.g.:

(define-fun f ((color Int) (sortAsc Int) (sortDesc Int)) Int (ite (<= 1 sortAsc) (ite (<= 1 sortDesc) 0 2) 3))

where ite stands for if-then-else. I can do a simple preprocessing to match Lisp or another syntax. What I need is the value of f with specific arguments. I prefer something off-the-shelf rather than writing yet another prefix notation calculator in Python.

2

Let me ask why you are not using a lisp program to run the lisp code?

3

Because I’m using Python code, e.g. cvc5, which produces Lisp code.

4

I found Hy, which can do it:

import hy

s = '''
(setv color 1)
(setv sortAsc 3)
(setv sortDesc 0)
(defn f [color sortAsc sortDesc] (if (<= 1 sortAsc) (if (<= 1 sortDesc) 0 2) 3))
(f color sortAsc sortDesc)
'''

print(hy.eval(hy.read_many(s)))

The author recommended something simpler, e.g. Scheme implementation. Searching PyPi for Scheme doesn’t help, though. Any recommendations?

2 Likes
5

I wonder if this would be a good moment to try your hand at writing a very simple Lisp interpreter in Python? It shouldn’t be too hard to design a simplistic parser that supports a subset of Lisp functionality, and it’s an excellent exercise.

6

Maybe, but I have too much work to do. As I wrote in my post: “I prefer something off-the-shelf rather than writing yet another prefix notation calculator in Python.”

7

Yeah I saw that, but having looked for something off-the-shelf and found little, it may be worth reconsidering.

8

But it outputs lisp. There is nothing to say that you can not use more then one language in your work.

9

tkinter waves shyly and glances down at the complete Tcl interpreter bundled with your GUI library…

1 Like
10

Have a look at Lispy and if you feel you have to use lisp try Steel Bank Common Lisp

11

Thanks. Lispy is on the top of my list of DIY options. I tested cl4py which uses sbc backend, but had some issues with it and went with Hy for now.

12

i didn’t understand this! can u rephrase a bit?

13

Searching PyPi for Scheme (Search results · PyPI) yields completely irrelevant results about various schemas.