diff --git a/compiler/chapter_1.md b/compiler/chapter_1.md index 7fcba76..db5dd6c 100644 --- a/compiler/chapter_1.md +++ b/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. -5. \*\* Rewrite parser, to use infix notation (`1 + 2 * 3`) instead of prefix/polish notation (`+ 1 * 2 3`). +2. \* Add position (line and column number) to each expression. +3. \*\* Rewrite parser, to use infix notation (`1 + 2 * 3`) instead of prefix/polish notation (`+ 1 * 2 3`). ## 1.5 Putting it together diff --git a/compiler/chapter_3.md b/compiler/chapter_3.md index c9133a3..ff75ad3 100644 --- a/compiler/chapter_3.md +++ b/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 diff --git a/compiler/chapter_4.md b/compiler/chapter_4.md index 3bc464f..34ebd42 100644 --- a/compiler/chapter_4.md +++ b/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" }); }