Problem 44382. Parse me a Lisp

Created by @bmtran (Bryant Tran)

Solve Later

Description

In Lisp and its variants, function calls are done using parenthesis where the first item in the parenthesis is the function being called and the following items are arguments to the function. Given a mathematical ( + - * / ) expression using this notation, return the result. Note: In Lisp, functions that normally take only two arguments can be called with many arguments, with the function being applied to all elements from left to right.

Simple example

(+ 1 1 1 1 1)

would give 5.

Complicated example

(* (* 10 (+ 1 4)) (+ 10 (/ 12 2 3) 1) 0.1)

would give 65.

Solve

Solution Stats

Last solution submitted on Oct 08, 2019

Last 200 Solutions

Problem Comments

2 Comments

2 Comments

Alfonso Nieto-Castanon on 19 Oct 2017

it seems look-up table solutions are becoming a bit of an issue, could you please add a few test cases to discourage this? +1 for random test cases that are a bit harder to trick, for example something like n=randi(100,1,randi(10)); expr = "(+" + string(num2str(n))+ ")"; assert(isequal(eval_lisp(expr), sum(n)));

James on 11 Dec 2017

I think another test case with multiple expressions would be equally useful. Even something as simple as (+ 1 (* 2 3) 4) would prevent some of the look-up solutions. Make some of those values random, and it will work even better.

Solution Comments

Solution 1312667

1 Comment

1 Comment

James on 11 Dec 2017

Nice. I was trying to figure out how to use strtok, but couldn't quite come up with it.

Solution 1292106

3 Comments

3 Comments

T. Dunker on 17 Oct 2017

Are you sure that your Test Suite works? I had to change all the double quotes to single quotes.

@bmtran (Bryant Tran) on 18 Oct 2017

Double-quoted strings are string literals in MATLAB R2017a+. To convert a string to char array, use the "char" function.

James on 11 Dec 2017

Thank you for that hint about the "char", bmtran. Never would have figured out what was wrong with my solution otherwise...

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