# [racket] What is the equivalent of ToExpression in Mathematica?

On Wed, Feb 29, 2012 at 4:33 PM, Ashok Bakthavathsalam
<ashokb at kggroup.com> wrote:
>* Will eval-string work even if the string is the normal mathematical
*>* notation?
*>* For example, "1+1" or "8*74-2" ?
*
No, but there is an example in Racket's parser-tools library
(parser-tools/examples/calc) that will parse very simple arithmetic
expressions.
https://github.com/plt/racket/blob/master/collects/parser-tools/examples/calc.rkt
It's not provided as a reusable library, unfortunately. Still, here's
a quick-and-dirty example just to show what it can do:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
#lang racket
;; Let's break abstractions! Muhahaha...
(require (only-in rackunit require/expose))
(require/expose parser-tools/examples/calc (calc))
;; You'll see some output (1 and -2) up front: that's the test code
from loading the calc module.
;; Ignore it.
(printf "What's 3 + 4?\n")
(calc (open-input-string "3 + 4"))
(printf "also:\n")
(calc (open-input-string "8*74-2"))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
When you run this, you'll see that calc is hardcoded to print some
test values up front. What makes it somewhat un-reusable is the fact
that it isn't really a function: 'calc' prints to screen, rather than
return its computed value.
It shouldn't be too hard to clean up the example and make it a reusable library.