Finish chapter 5

compiler/chapter_1.md

@@ -266,8 +266,8 @@ The implemented parser goes through each token and checks the structure of the p
 #### Exercises
 
 1. Implement subtraction and division.
-3. \* Add position (line and column number) to each expression.
+2. \* Add position (line and column number) to each expression.
-5. \*\* Rewrite parser, to use infix notation (`1 + 2 * 3`) instead of prefix/polish notation (`+ 1 * 2 3`).
+3. \*\* Rewrite parser, to use infix notation (`1 + 2 * 3`) instead of prefix/polish notation (`+ 1 * 2 3`).
 
 ## 1.5 Putting it together
 

compiler/chapter_3.md

@@ -564,6 +564,10 @@ class Parser {
             return this.expr({ type: "if", cond, truthy }, pos);
         }
         this.step();
+        if (this.test("if")) {
+            const falsy = this.parseIf();
+            return this.expr({ type: "if", cond, truthy, falsy }, pos);
+        }
         if (!this.test("{")) {
             this.report("expected block");
             return this.expr({ type: "error" }, pos);
@@ -577,7 +581,7 @@ class Parser {
 
 When parsing an if-expression, we assume we already have reached an `if`-token.
 
-We skip the `if`-token. Then we parse the condition expression `cond`. Then we check for a `{`-token and parse block. Then we check for an `else`-token. If not present, we return an if-expression with no `falsy`-option. Else we skip the `else`-token, check for and parse the `falsy`-block, and return the if-expression with the `falsy`-option.
+We skip the `if`-token. Then we parse the condition expression `cond`. Then we check for a `{`-token and parse block. Then we check for an `else`-token. If not present, we return an if-expression with no `falsy`-option. Else we skip the `else`-token. If we find a `if`-token, it means we're parsing an else-if construct, in which case we parse an if expression recursively. Else check for and parse the `falsy`-block. And then return the if-expression with the `falsy`-option.
 
 ## 3.8 Loop expressions
 

compiler/chapter_4.md

@@ -973,7 +973,7 @@ class Evaluator {
     // ...
     private executeBuiltin(name: string, args: Value[], syms: Syms): Flow {
         // ...
-        if (name === "push") {
+        if (name === "array_push") {
             if (args.length !== 2)
                 throw new Error("incorrect arguments");
             const array = args[0];
@@ -991,7 +991,69 @@ class Evaluator {
 
 This function expects that the first parameter is an array, and the second is the value to push.
 
-### 4.8.3 Println
+### 4.8.3 Array length
+
+
+We'll also need a way to get the length of an array.
+
+```ts
+class Evaluator {
+    // ...
+    private executeBuiltin(name: string, args: Value[], syms: Syms): Flow {
+        // ...
+        if (name === "array_len") {
+            if (args.length !== 1)
+                throw new Error("incorrect arguments");
+            const array = args[0];
+            if (array.type !== "array")
+                throw new Error("incorrect arguments");
+            return flowValue({ type: "int", value: array.values.length });
+        }
+        // ...
+    }
+    // ...
+}
+```
+
+### 4.8.3 String functions
+
+Like arrays, we need push and length functions for strings too.
+
+```ts
+class Evaluator {
+    // ...
+    private executeBuiltin(name: string, args: Value[], syms: Syms): Flow {
+        // ...
+        if (name === "string_concat") {
+            if (args.length !== 2)
+                throw new Error("incorrect arguments");
+            if (args[0].type === "string") {
+                if (args[1].type === "string")
+                    return flowValue({ type: "string", value: args[0].value + args[1].value });
+                if (args[1].type === "int")
+                    return flowValue({ type: "string", value: args[0].value + String.fromCharCode(args[1].value) });
+            }
+            if (args[0].type === "int" && args[1].type === "string") {
+                return flowValue({ type: "string", value: String.fromCharCode(args[0].value) + args[1].value });
+            }
+            throw new Error("incorrect arguments");
+        }
+        if (name === "string_len") {
+            if (args.length !== 1)
+                throw new Error("incorrect arguments");
+            if (args[0].type !== "string")
+                throw new Error("incorrect arguments");
+            return flowValue({ type: "int", value: args[0].value.length });
+        }
+        // ...
+    }
+    // ...
+}
+```
+
+The function `string_concant` takes either two strings or a string and a character (int). A new string is returning containing both values concatonated.
+
+### 4.8.4 Println
 
 To print text to the screen, we need a print function. We'll make one called `println` which will also print a newline afterwards.
 
@@ -1031,7 +1093,7 @@ println("hello {}", a);
 println("{} + {} = {}", 1, 2, 1 + 2);
 ```
 
-### 4.8.4 Exit
+### 4.8.5 Exit
 
 Normally, the evaluator will return a zero-exit code, meanin no error. In case we program should result in an error code, we'll need an exit function.
 
@@ -1056,7 +1118,52 @@ class Evaluator {
 }
 ```
 
-### 4.8.5 Define builtins
+### 4.8.6 Convert values to strings
+
+This function will return a string representation of any value.
+
+```ts
+class Evaluator {
+    // ...
+    private executeBuiltin(name: string, args: Value[], syms: Syms): Flow {
+        // ...
+        if (name === "to_string") {
+            if (args.length !== 1)
+                throw new Error("incorrect arguments");
+            return flowValue({ type: "string", value: valueToString(args[0]) });
+        }
+        // ...
+    }
+    // ...
+}
+```
+
+### 4.8.7 Convert strings to integers
+
+This function will try to convert a string into an integer.
+
+```ts
+class Evaluator {
+    // ...
+    private executeBuiltin(name: string, args: Value[], syms: Syms): Flow {
+        // ...
+        if (name === "string_to_int") {
+            if (args.length !== 1 || args[0].type !== "string")
+                throw new Error("incorrect arguments");
+            const value = parseInt(args[0].value);
+            if (value === NaN)
+                return flowValue({ type: "null" });
+            return flowValue({ type: "int", value });
+        }
+        // ...
+    }
+    // ...
+}
+```
+
+The function will return a null value, in case conversion fails.
+
+## 4.9 Define builtins
 
 Finally, we need a way to define the builtin functions in the symbol table.
 
@@ -1066,7 +1173,10 @@ class Evaluator {
     public defineBuiltins() {
         this.root.define("array", { type: "builtin_fn", name: "array" });
         this.root.define("struct", { type: "builtin_fn", name: "struct" });
-        this.root.define("push", { type: "builtin_fn", name: "struct" });
+        this.root.define("array_push", { type: "builtin_fn", name: "array_push" });
+        this.root.define("array_len", { type: "builtin_fn", name: "array_len" });
+        this.root.define("string_concat", { type: "builtin_fn", name: "string_concat" });
+        this.root.define("string_len", { type: "builtin_fn", name: "string_len" });
         this.root.define("println", { type: "builtin_fn", name: "println" });
         this.root.define("exit", { type: "builtin_fn", name: "exit" });
     }