feat: Implement Chapter 10 (Functions) (#21)

Implementation of [Chapter 10] of _Crafting Interpreters_.

I wondered back in #10 whether I'd be shooting myself in the foot by
supporting `,` as a number separator (`1,234`). This is where it
happened. The comma becomes quite ambiguous in the arguments list of a
function call. For exmaple:

```
f(1,234,567);
```

Is that a call to `f` with a single argument, `1,234,567` or a call to
`f` with three arguments, `1`, `234` and `567`? The grammar is
ambiguous.

My solution is to make spaces significant while scanning:

```
f(1,234,567);  // one argument
f(1, 234, 567);  // three arguments
```

We'll see how this holds up!

[Chapter 10]: https://craftinginterpreters.com/functions.html

.eslintrc.cjs

@@ -45,6 +45,14 @@ module.exports = {
 				// Disable autofixing "let" -> "const" just because I haven't mutated it _yet_.
 				// Autofixing `() => fn()` -> `() => { fn() }` is a recipe for trouble.
 				"@typescript-eslint/no-confusing-void-expression": "off",
+				"@typescript-eslint/no-unnecessary-condition": [
+					"error",
+					{
+						// why isn't this the default?
+						// https://github.com/typescript-eslint/typescript-eslint/issues/7047
+						allowConstantLoopConditions: true,
+					},
+				],
 				"no-autofix/@typescript-eslint/no-confusing-void-expression": "warn",
 				"no-autofix/prefer-const": "warn",
 				"perfectionist/sort-interfaces": "off",

baselines/chapter10-add-abc.txt

@@ -0,0 +1,2 @@
+6
+nil

baselines/chapter10-define-and-call-fun.txt

@@ -0,0 +1 @@
+Hi, Dear Reader!

baselines/chapter10-fibonacci.txt

@@ -0,0 +1,20 @@
+0
+1
+1
+2
+3
+5
+8
+13
+21
+34
+55
+89
+144
+233
+377
+610
+987
+1597
+2584
+4181

baselines/chapter10-make-counter.txt

@@ -0,0 +1,2 @@
+1
+2

baselines/chapter10-multi-currency.txt

@@ -0,0 +1,2 @@
+$100,000 at 7% for 10 years:
+196715.1357289567

baselines/chapter10-print-fun.txt

@@ -0,0 +1 @@
+<fn f>

baselines/chapter10-return-in-loop.txt

@@ -0,0 +1,2 @@
+1
+2

baselines/chapter10-return-nothing.txt

@@ -0,0 +1,2 @@
+don't return anything
+nil

baselines/chapter10-too-many-params.errors.txt

@@ -0,0 +1,10 @@
+[line 32] Error at 'p255': Can't have more than 255 parameters.
+[line 32] Error at 'p256': Can't have more than 255 parameters.
+[line 32] Error at 'p257': Can't have more than 255 parameters.
+[line 32] Error at 'p258': Can't have more than 255 parameters.
+[line 32] Error at 'p259': Can't have more than 255 parameters.
+[line 64] Error at '255': Can't have more than 255 arguments.
+[line 64] Error at '256': Can't have more than 255 arguments.
+[line 64] Error at '257': Can't have more than 255 arguments.
+[line 64] Error at '258': Can't have more than 255 arguments.
+[line 64] Error at '259': Can't have more than 255 arguments.

examples/chapter10-add-abc.lox

@@ -0,0 +1,5 @@
+fun add(a, b, c) {
+  print a + b + c;
+}
+
+print add(1, 2, 3);

examples/chapter10-clock.lox

@@ -0,0 +1,4 @@
+print clock;
+var start = clock();
+var end = clock();
+print end - start;  // hopefully 0!

examples/chapter10-define-and-call-fun.lox

@@ -0,0 +1,5 @@
+fun sayHi(first, last) {
+  print "Hi, " + first + " " + last + "!";
+}
+
+sayHi("Dear", "Reader");

examples/chapter10-fibonacci.lox

@@ -0,0 +1,8 @@
+fun fib(n) {
+  if (n <= 1) return n;
+  return fib(n - 2) + fib(n - 1);
+}
+
+for (var i = 0; i < 20; i = i + 1) {
+  print fib(i);
+}

examples/chapter10-make-counter.lox

@@ -0,0 +1,13 @@
+fun makeCounter() {
+  var i = 0;
+  fun count() {
+    i = i + 1;
+    print i;
+  }
+
+  return count;
+}
+
+var counter = makeCounter();
+counter(); // "1".
+counter(); // "2".

examples/chapter10-multi-currency.lox

@@ -0,0 +1,10 @@
+fun compound(amount, rate, years) {
+    var p = 1 + rate / 100;
+    for (var i = 0; i < years; i = i + 1) {
+        amount = amount * p;
+    }
+    return amount;
+}
+
+print "$100,000 at 7% for 10 years:";
+print compound($100,000, 7, 10);

examples/chapter10-print-fun.lox

@@ -0,0 +1,3 @@
+fun f() {}
+
+print f;

examples/chapter10-return-in-loop.lox

@@ -0,0 +1,9 @@
+fun count(n) {
+  while (n < 100) {
+    if (n == 3) return n; // <--
+    print n;
+    n = n + 1;
+  }
+}
+
+count(1);

examples/chapter10-return-nothing.lox

@@ -0,0 +1,6 @@
+fun procedure() {
+  print "don't return anything";
+}
+
+var result = procedure();
+print result; // ?

examples/chapter10-too-many-params.lox

@@ -0,0 +1,65 @@
+// for i in range(0, 26):
+//   for j in range(0, 10):
+//     print(f"p{10*i+j},", end='')
+//   print()
+
+fun tooManyParams(
+  p0,  p1,  p2,  p3,  p4,  p5,  p6,  p7,  p8,  p9,
+ p10, p11, p12, p13, p14, p15, p16, p17, p18, p19,
+ p20, p21, p22, p23, p24, p25, p26, p27, p28, p29,
+ p30, p31, p32, p33, p34, p35, p36, p37, p38, p39,
+ p40, p41, p42, p43, p44, p45, p46, p47, p48, p49,
+ p50, p51, p52, p53, p54, p55, p56, p57, p58, p59,
+ p60, p61, p62, p63, p64, p65, p66, p67, p68, p69,
+ p70, p71, p72, p73, p74, p75, p76, p77, p78, p79,
+ p80, p81, p82, p83, p84, p85, p86, p87, p88, p89,
+ p90, p91, p92, p93, p94, p95, p96, p97, p98, p99,
+p100,p101,p102,p103,p104,p105,p106,p107,p108,p109,
+p110,p111,p112,p113,p114,p115,p116,p117,p118,p119,
+p120,p121,p122,p123,p124,p125,p126,p127,p128,p129,
+p130,p131,p132,p133,p134,p135,p136,p137,p138,p139,
+p140,p141,p142,p143,p144,p145,p146,p147,p148,p149,
+p150,p151,p152,p153,p154,p155,p156,p157,p158,p159,
+p160,p161,p162,p163,p164,p165,p166,p167,p168,p169,
+p170,p171,p172,p173,p174,p175,p176,p177,p178,p179,
+p180,p181,p182,p183,p184,p185,p186,p187,p188,p189,
+p190,p191,p192,p193,p194,p195,p196,p197,p198,p199,
+p200,p201,p202,p203,p204,p205,p206,p207,p208,p209,
+p210,p211,p212,p213,p214,p215,p216,p217,p218,p219,
+p220,p221,p222,p223,p224,p225,p226,p227,p228,p229,
+p230,p231,p232,p233,p234,p235,p236,p237,p238,p239,
+p240,p241,p242,p243,p244,p245,p246,p247,p248,p249,
+p250,p251,p252,p253,p254,p255,p256,p257,p258,p259
+) {
+    return 260;
+}
+
+// note: whitespace is important here!!
+print tooManyParams(
+  0,   1,   2,   3,   4,   5,   6,   7,   8,   9,
+ 10,  11,  12,  13,  14,  15,  16,  17,  18,  19,
+ 20,  21,  22,  23,  24,  25,  26,  27,  28,  29,
+ 30,  31,  32,  33,  34,  35,  36,  37,  38,  39,
+ 40,  41,  42,  43,  44,  45,  46,  47,  48,  49,
+ 50,  51,  52,  53,  54,  55,  56,  57,  58,  59,
+ 60,  61,  62,  63,  64,  65,  66,  67,  68,  69,
+ 70,  71,  72,  73,  74,  75,  76,  77,  78,  79,
+ 80,  81,  82,  83,  84,  85,  86,  87,  88,  89,
+ 90,  91,  92,  93,  94,  95,  96,  97,  98,  99,
+100, 101, 102, 103, 104, 105, 106, 107, 108, 109,
+110, 111, 112, 113, 114, 115, 116, 117, 118, 119,
+120, 121, 122, 123, 124, 125, 126, 127, 128, 129,
+130, 131, 132, 133, 134, 135, 136, 137, 138, 139,
+140, 141, 142, 143, 144, 145, 146, 147, 148, 149,
+150, 151, 152, 153, 154, 155, 156, 157, 158, 159,
+160, 161, 162, 163, 164, 165, 166, 167, 168, 169,
+170, 171, 172, 173, 174, 175, 176, 177, 178, 179,
+180, 181, 182, 183, 184, 185, 186, 187, 188, 189,
+190, 191, 192, 193, 194, 195, 196, 197, 198, 199,
+200, 201, 202, 203, 204, 205, 206, 207, 208, 209,
+210, 211, 212, 213, 214, 215, 216, 217, 218, 219,
+220, 221, 222, 223, 224, 225, 226, 227, 228, 229,
+230, 231, 232, 233, 234, 235, 236, 237, 238, 239,
+240, 241, 242, 243, 244, 245, 246, 247, 248, 249,
+250, 251, 252, 253, 254, 255, 256, 257, 258, 259
+);

package.json

@@ -28,7 +28,7 @@
 		"lint:package-json": "npmPkgJsonLint .",
 		"lint:packages": "pnpm dedupe --check",
 		"lint:spelling": "cspell \"**\" \".github/**/*\"",
-		"pre-push": "pnpm run '/^lint(?!:packages).*$/'",
+		"pre-push": "pnpm run '/^(tsc|lint(?!:packages).*)$/'",
 		"prepare": "husky install",
 		"repl": "pnpm run:ts src/index.ts",
 		"run:ts": "node --loader ts-node/esm --no-warnings",

src/ast-printer.ts

@@ -14,7 +14,14 @@ export const astPrinter: ExpressionVisitor<string> & StmtVisitor<string> = {
 			"block",
 			...block.statements.map((stmt) => visitStmt(stmt, astPrinter)),
 		),
+	call: (expr) => parenthesize(expr.callee, ...expr.args),
 	expr: (stmt) => visitExpr(stmt.expression, astPrinter),
+	func: (stmt) =>
+		parenthesizeText(
+			"func",
+			parenthesizeText(stmt.name.lexeme, ...stmt.params.map((p) => p.lexeme)),
+			visitStmt({ kind: "block", statements: stmt.body }, astPrinter),
+		),
 	grouping: (expr) => parenthesize("group", expr.expr),
 	if: (stmt) =>
 		parenthesizeText(
@@ -26,6 +33,7 @@ export const astPrinter: ExpressionVisitor<string> & StmtVisitor<string> = {
 	literal: (expr) => (expr.value === null ? "nil" : String(expr.value)),
 	logical: (expr) => parenthesize(expr.operator.lexeme, expr.left, expr.right),
 	print: (stmt) => parenthesize("print", stmt.expression),
+	return: (stmt) => parenthesize("return", ...(stmt.value ? [stmt.value] : [])),
 	unary: (expr) => parenthesize(expr.operator.lexeme, expr.right),
 	"var-expr": (expr) => String(expr.name.literal),
 	"var-stmt": (stmt) =>
@@ -49,8 +57,8 @@ function parenthesizeText(...parts: (null | string)[]) {
 
 // This would be nicer if it could be (Expr | Stmt)… but there's no programmatic
 // way to distinguish those two in order to tell which visit function to call.
-function parenthesize(name: string, ...exprs: (Expr | string)[]) {
-	const parts = [name];
+function parenthesize(...exprs: (Expr | string)[]) {
+	const parts = [];
 	for (const expr of exprs) {
 		parts.push(typeof expr == "string" ? expr : visitExpr(expr, astPrinter));
 	}

src/ast.ts

@@ -35,6 +35,15 @@ export interface VarExpr {
 	name: Token;
 }
 
+export interface Call {
+	kind: "call";
+	callee: Expr;
+	paren: Token;
+	args: Expr[];
+}
+
+// Statements
+
 export interface Assign {
 	kind: "assign";
 	name: Token;
@@ -76,15 +85,37 @@ export interface While {
 	body: Stmt;
 }
 
+export interface Func {
+	kind: "func";
+	name: Token;
+	params: Token[];
+	body: Stmt[];
+}
+
+export interface Return {
+	kind: "return";
+	keyword: Token;
+	value: Expr | null;
+}
+
 export type Expr =
 	| Assign
 	| Binary
+	| Call
 	| Grouping
 	| Literal
 	| Logical
 	| Unary
 	| VarExpr;
-export type Stmt = Block | Expression | IfStmt | Print | VarStmt | While;
+export type Stmt =
+	| Block
+	| Expression
+	| Func
+	| IfStmt
+	| Print
+	| Return
+	| VarStmt
+	| While;
 
 export type ExpressionVisitor<R> = {
 	[Kind in Expr["kind"]]: (expr: Extract<Expr, { kind: Kind }>) => R;

src/callable.ts

@@ -0,0 +1,6 @@
+import { Interpreter } from "./interpreter.js";
+
+export abstract class LoxCallable {
+	abstract arity(): number;
+	abstract call(interpreter: Interpreter, args: unknown[]): unknown;
+}