Racket language: How to convert string to variable-name

Question

I am pretty new in Racket and I have tried to run Chris Jester-Young's solution (How to convert string to variable-name in scheme) to convert string to variable name (and its converse, in other words, conversing variable name to string):

#lang racket
(define-syntax string->variable-name
   (lambda (stx)
   (syntax-case stx ()
     ((_ str)
       (string? (syntax->datum #'str))
         (datum->syntax #'str (string->symbol (syntax->datum #'str)))))))

(define-syntax variable-name->string
  (lambda (stx)
    (syntax-case stx ()
    ((_ id)
       (identifier? #'id)
         (datum->syntax #'id (symbol->string (syntax->datum #'id)))))))

It was fine for variable-name->string, here an example:

>(define myvar 10)
>(variable-name->string myvar)
  "myvar"

However, I had no success with string->variable-name:

>(define (string->variable-name "myvar2") 4)
    error define: not an identifier, identifier with default, or keyword
    for procedure argument in: "myvar2"

I am using Racket 6.6, linux mint 17.3 64bits.

My main goal is how to convert a string to a variable name (identifier).

I was wondering:

to read a text file;
to get the name of the variables (string) from that text file; and
to use define to set the variable names with random integers.

Any help I will appreciate.

Use (variable-name->string foo) to invoke a macro with the name variable-name->string. The (define (variable-name->string ... means that you are defining a function named variable-name->string and since "myvar2" is not a legal name for a function argument, you get an error. — soegaard
– soegaard, Commented Aug 17, 2016 at 11:14
What are you trying to do with this? The macro that changes from a variable to a string does so compile time. The other way needs to be aswell so you can never make anything useful with these later. — Sylwester
– Sylwester, Commented Aug 17, 2016 at 12:32
Reading plain text file is a requirement for an academic work. Moreover, I have to build a program which is able to: 1- read a plain text file; 2- extract some strings from that plain text file; 3- assign that strings to variable names, dynamically; 4- do some calculation with that variables; and 5- finally, write down the outcomes to a plain text file. I have got success in all those steps, in exception with step 3. — Alex Correia
– Alex Correia, Commented Aug 17, 2016 at 21:53
Hope you have learned what's happening. @soegaard 's response is correct; just call (define myvar2 1) before the other call — Monty _s Flying Circus
– Monty _s Flying Circus, Commented Aug 15, 2018 at 0:23

Community · Accepted Answer · 2017-05-23 10:28:38Z

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You may check answers from here.

I was advised not to use strings but identifiers. So instead of having a plain text file you may use another Racket source with identifiers you want to use and just import this one.

edited May 23, 2017 at 10:28

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answered Aug 17, 2016 at 12:56

Bohdan Ivanov

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2 Comments

Alex Correia Over a year ago

Reading plain text file is a requirement for an academic work. Moreover, I have to build a program which is able to: 1- read a plain text file; 2- extract some strings from that plain text file; 3- assign that strings to variable names, dynamically; 4- do some calculation with that variables; and 5- finally, write down the outcomes to a plain text file. I have got success in all those steps, in exception with step 3.

Alex Correia Over a year ago

Trying to give more details of what I am trying to do: (define temp_var "Xi") ;the string "Xi" was extracted from a text file. (define (display temp_var) 2 ) ;is it the same of (define Xi 2)? (display Xi) ;error Xi was not defined. (+ Xi 3) ; is the outcome equals to 5?

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