feat: add Text.from(Var)Array (#674)

Using `fromIter` is probably less-than-optimal performance-wise, but we
can add a compiler primitive if it proves to become a bottleneck. For
now it fills a hole that I perceived in the Motoko AI hackathon.

Adds test for both `Text.fromArray` and `fromVarArray`.

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.13.x
+
+* Added `Text.fromArray` and `Text.fromVarArray` functions (#674).
+
 ## 0.13.4
 
 * Breaking change (minor): `Float.format(#hex)` is no longer supported. 

src/Text.mo

@@ -44,6 +44,26 @@ module {
   /// ```
   public let fromChar : (c : Char) -> Text = Prim.charToText;
 
+  /// Converts the given `[Char]` to a `Text` value.
+  ///
+  /// ```motoko include=import
+  /// let text = Text.fromArray(['A', 'v', 'o', 'c', 'a', 'd', 'o']); // "Avocado"
+  /// ```
+  ///
+  /// Runtime: O(a.size())
+  /// Space: O(a.size())
+  public func fromArray(a : [Char]) : Text = fromIter(a.vals());
+
+  /// Converts the given `[var Char]` to a `Text` value.
+  ///
+  /// ```motoko include=import
+  /// let text = Text.fromVarArray([var 'E', 'g', 'g', 'p', 'l', 'a', 'n', 't']); // "Eggplant"
+  /// ```
+  ///
+  /// Runtime: O(a.size())
+  /// Space: O(a.size())
+  public func fromVarArray(a : [var Char]) : Text = fromIter(a.vals());
+
   /// Iterates over each `Char` value in the given `Text`.
   ///
   /// Equivalent to calling the `t.chars()` method where `t` is a `Text` value.
@@ -76,7 +96,7 @@ module {
       func _ {
         switch (cs.next()) {
           case (?c) { c };
-          case (null) { Prim.trap("Text.toArray") };
+          case null { Prim.trap("Text.toArray") };
         };
       }
     )

test/Text.test.mo

@@ -1038,6 +1038,16 @@ run(
         "toArray-example",
         Array.freeze(Text.toVarArray("Café")),
         M.equals(T.array<Char>(T.charTestable, ['C', 'a', 'f', 'é']))
+      ),
+      test(
+        "fromArray-example",
+        Text.fromArray(['A', 'v', 'o', 'c', 'a', 'd', 'o']),
+        M.equals(T.text "Avocado")
+      ),
+      test(
+        "fromVarArray-example",
+        Text.fromVarArray([var 'E', 'g', 'g', 'p', 'l', 'a', 'n', 't']),
+        M.equals(T.text "Eggplant")
       )
     ]
   )