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

:::note 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

• Char
• Text
• Iter