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10913 :: 'can have side effects' error.

• AntonioFS (orginal) [2024-01-24T14:08:03+01:00] view original

  Hello.

  I am "stuck" in my learning of Nim. In the attached code, I don't know how to get rid of the error: 'introduccionValoresEnCampos' can have side effects.

  Would you be so kind as to review the code to know why I get this error in the function in question?

  Best regards. Antonio F.S.

  ---

  import std/rdstdin import std/strutils

  const

  TIPO_ANIMAL : string = "Perro=1 || Gato=2: " DATOS_INCORRECTOS : string = "< Entrada no válida >" PERRO : string = "< El tipo de animal es Perro >" GATO : string = "< El tipo de animal es Gato >" ANIMAL_INCORRECTO : string = "< El tipo de animal es incorrecto"

  var

  nombre: seq[string] = @[] tipo: seq[string] = @[] edad: seq[int] = @[]

  func introduccionValoresEnCampos(): (seq[string], seq[string], seq[int]) =

  var

  numTipo : int = 0 entrada : string = "" ok : bool = false

  while true :

  ok = readLineFromStdin(TIPO_ANIMAL, entrada)

  try:

  numTipo = parseInt(entrada)

  except ValueError:

  echo DATOS_INCORRECTOS continue

  case numTipo

  of 1:

  echo PERRO nombre.add("Loki") tipo.add("Perro") edad.add(1) break

  of 2:

  echo GATO nombre.add("Tim") tipo.add("Gato") edad.add(2) break

  else:

  echo ANIMAL_INCORRECTO

  return (nombre, tipo, edad)

  proc entrarDatosAnimales*() =

  (nombre, tipo, edad) = introduccionValoresEnCampos()

---

• AntonioFS (orginal) [2024-01-24T14:14:53+01:00] view original

  Hi.

  Hello

  It seems that the code has lost its formatting when sending the message. Is it possible to attach the source file?

  Best regards. Antonio F.S.

---

• PMunch (orginal) [2024-01-24T14:27:31+01:00] view original

  You seem a bit confused with the concept of proc vs. func. In Nim a proc is a procedure which is what most imperative languages incorrectly calls a function, and func is the more pure mathematical concept of a function. As such a func can't have side-effects, the same inputs should always yield the same outputs, and there shouldn't be any hidden changes made to anything else. Your func introduccionValoresEnCampos breaks both of these rules. Since it reads from standard input the output can change each time you run it, depending on what the user writes. And since you add to your three sequences you are also changing something which isn't your return value. If you either change introduccionValoresEnCampos to be a proc this will work. The alternative is to move the three sequences from the global scope and into the introduccionValoresEnCampos function and move the readLineFromStdin call out to the entrarDatosAnimales and pass the string in as an argument. This would of course mean that it wouldn't return an increasingly growing set of sequences, so you would have to also do that stitching elsewhere.

---

• AntonioFS (orginal) [2024-01-24T14:40:15+01:00] view original

  Hello.

  It is clear that such concepts are not too understandable for me with Nim.

  I will study your reply, for which I am very grateful.

  Best regards. AntonioF.S.

---

• AntonioFS (orginal) [2024-01-24T18:13:38+01:00] view original

  Hello.

  Actually my approach was wrong because no function was needed in this case. The thing is that changing the mindset from one language to another takes time and effort. But it has helped me a lot to realise that in Nim functions have a correctly strict semantic connotation.

  The code (if you are kind enough to reformat it) will look like below.

  Thank you very much (I continue with my study of Nim).

  Best regards. Antonio F.S.

  ---

  import std/rdstdin import std/strutils

  const

  TIPO_ANIMAL : string = "Perro=1 || Gato=2: " DATOS_INCORRECTOS : string = "< Entrada no válida >" PERRO : string = "< El tipo de animal es Perro >" GATO : string = "< El tipo de animal es Gato >" ANIMAL_INCORRECTO : string = "< El tipo de animal es incorrecto"

  var

  nombre: seq[string] = @[] tipo: seq[string] = @[] edad: seq[int] = @[]

  proc introduccionValoresEnCampos() =

  var

  numTipo : int = 0 entrada : string = "" ok : bool = false

  while true :

  ok = readLineFromStdin(TIPO_ANIMAL, entrada)

  try:

  numTipo = parseInt(entrada)

  except ValueError:

  echo DATOS_INCORRECTOS continue

  case numTipo

  of 1:

  echo PERRO nombre.add("Loki") tipo.add("Perro") edad.add(1) break

  of 2:

  echo GATO nombre.add("Tim") tipo.add("Gato") edad.add(2) break

  else:

  echo ANIMAL_INCORRECTO

  proc verDatosVectores() =

  for i in 0..high(nombre):

  echo "Nombre: ", nombre[i] echo "Tipo: ", tipo[i] echo "Edad: ", edad[i] echo "n"

  introduccionValoresEnCampos() verDatosVectores()

---