add string documentation

README.md

@@ -20,16 +20,17 @@ The language is based off of the Monkey language from the book [Writing an Inter
 1. [Variables](#variables)
 2. [Arrays](#arrays)
 3. [Dictionaries](#dictionaries)
-4. [Functions](#functions)
-5. [Blocks](#blocks)
-6. [Conditionals](#conditionals)
-7. [Loops](#loops)
-8. [Scoping](#scoping)
-9. [Returning values](#returning-values)
-10. [Object Oriented Programming](#object-oriented-programming)
-11. [Comments](#comments)
-12. [Built-in functions](#built-in-functions)
-13. [Examples](#examples)
+4. [Strings](#strings)
+5. [Functions](#functions)
+6. [Blocks](#blocks)
+7. [Conditionals](#conditionals)
+8. [Loops](#loops)
+9. [Scoping](#scoping)
+10. [Returning values](#returning-values)
+11. [Object Oriented Programming](#object-oriented-programming)
+12. [Comments](#comments)
+13. [Built-in functions](#built-in-functions)
+14. [Examples](#examples)
 
 ### Variables
 
@@ -114,6 +115,30 @@ b[0] = 10;
 a; // [10, 2, 3]
 ```
 
+### Strings
+
+Strings are declared with double quotes `""`.
+
+```js
+let a = "hello";
+let b = "world";
+a + " " + b; // hello world
+```
+
+You can access characters in a string using square brackets.
+
+```js
+let a = "hello";
+print("I like to " + a[1] + "at");// I like to eat
+```
+
+However, strings are immutable. This means that you can't change a character in a string.
+
+```js
+let a = "hello";
+a[0] = "H"; // This will throw an error
+```
+
 ### Dictionaries
 
 Similar to other programming languages, Espresso supports key value pairs via dictionaries.
@@ -443,6 +468,8 @@ Espresso comes with a few built-in functions.
 - `print`: Prints a value to the console.
 - `push`: Pushes a value to the end of an array.
 - `pop`: Pops a value from the end of an array by default. Takes an optional index to pop from that instead.
+- `dict`: Creates an empty dictionary.
+- `str`: Converts a value to a string.
 
 ```js
 let count = len("hello"); // 5

src/utils.ts

@@ -49,15 +49,15 @@ export const asString = (value: any) => {
 
 export const isObject = (value: Expression | Value) => {
   if (value === null) {
-    return null
+    return false
   }
 
   switch (typeof value) {
     case 'string':
     case 'number':
     case 'boolean':
     case 'undefined':
-      return value
+      return false
   }
 
   return (