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Characters & text

Characters​

The Char type in Motoko represents a single Unicode character delimited with a single quotation mark (').

let letter : Char = 'A';
let symbol : Char = '✮';

// Comparing characters
'I' == 'i' // False
Iter

An Iter<T> is an object that sequentially produces values of specified type T until no more values remain.

import Char "mo:core/Char";

func reverse(t: Text) : Text {
  var result = "";
  for (c in t.chars()) {
    result := Char.toText(c) # result
  };
  result;
};

reverse("Motoko");

The operator # concatenates two Text values.

import Text "mo:core/Text";
import Iter "mo:core/Iter";
import Char "mo:core/Char";

persistent actor Alternator {

  // Turn text into an iterator of Char
  func textToChars(t: Text) : Iter.Iter<Char> {
    t.chars();
  };

  // Alternate capitalization
  public func alternateCaps(t: Text) : async Text {
    let chars = textToChars(t);
    var index = 0;
    // Apply a case function to each char
    let modified = Iter.map<Char, Text>(chars, func(c: Char) : Text {
      let charAsText = Char.toText(c);
      let transformedText =
        if (index % 2 == 0) {
          Text.toUpper(charAsText)
        } else {
          Text.toLower(charAsText)
        };
      index += 1;
      transformedText;
    });

    return Text.join("", modified);
  };
};
Conversions
  • Char can be converted to a single-character Text using Char.toText(c).
  • Char can be converted to its 32-bit Unicode scalar value using Char.toNat32(c).
  • A Char can be converted from a 32-bit Unicode scalar value using Char.fromNat32(n) (the function traps on invalid codes).

Text​

Strings of characters, familiar from other languages, are called text in Motoko, and represented using the Text type. A text value is an immutable sequence of Unicode characters delimited with a double quotation mark (").

let greeting : Text = "Hello, world!";

The # operator concatenates two Text values:

// Concatenating text

"ICP " # "❤️" # " Motoko" // "ICP ❤️ Motoko"

t.size() can be used to return the number of characters in the text t.

"abc".size() == 3

t.chars() returns an iterator enumerating the characters in t. For example:

import Char "mo:core/Char";
import Debug "mo:core/Debug";

for (c in "abc".chars()) {
  Debug.print(Char.toText(c));
}

Text values can be compared using "==", "<" and all the other relational operators.

Resources​