enhance: 数値リテラルの整数部分または小数部分の0を省略できるように

src/parser/scanner.ts

@@ -205,6 +205,10 @@ export class Scanner implements ITokenStream {
 				}
 				case '.': {
 					this.stream.next();
+					if (!this.stream.eof && digit.test(this.stream.char as string)) {
+						const digitToken = this.tryReadDigits(hasLeftSpacing, pos, true);
+						if (digitToken) return digitToken;
+					}
 					return TOKEN(TokenKind.Dot, pos, { hasLeftSpacing });
 				}
 				case '/': {
@@ -312,7 +316,7 @@ export class Scanner implements ITokenStream {
 					return TOKEN(TokenKind.CloseBrace, pos, { hasLeftSpacing });
 				}
 				default: {
-					const digitToken = this.tryReadDigits(hasLeftSpacing);
+					const digitToken = this.tryReadDigits(hasLeftSpacing, pos, false);
 					if (digitToken) return digitToken;
 
 					const wordToken = this.tryReadWord(hasLeftSpacing);
@@ -413,26 +417,30 @@ export class Scanner implements ITokenStream {
 		}
 	}
 
-	private tryReadDigits(hasLeftSpacing: boolean): Token | undefined {
+	private tryReadDigits(
+		hasLeftSpacing: boolean,
+		pos: { line: number, column: number },
+		hasLeadingDot: boolean,
+	): Token | undefined {
 		let wholeNumber = '';
 		let fractional = '';
 
-		const pos = this.stream.getPos();
-
-		while (!this.stream.eof && digit.test(this.stream.char)) {
-			wholeNumber += this.stream.char;
-			this.stream.next();
-		}
-		if (wholeNumber.length === 0) {
-			return;
+		if (!hasLeadingDot) {
+			while (!this.stream.eof && digit.test(this.stream.char)) {
+				wholeNumber += this.stream.char;
+				this.stream.next();
+			}
+			if (wholeNumber.length === 0) {
+				return;
+			}
 		}
-		if (!this.stream.eof && this.stream.char === '.') {
-			this.stream.next();
+		const decimalPoint = this.tryReadDecimalPoint(hasLeadingDot);
+		if (decimalPoint) {
 			while (!this.stream.eof as boolean && digit.test(this.stream.char as string)) {
 				fractional += this.stream.char;
 				this.stream.next();
 			}
-			if (fractional.length === 0) {
+			if (wholeNumber.length === 0 && fractional.length === 0) {
 				throw new AiScriptSyntaxError('digit expected', pos);
 			}
 		}
@@ -445,6 +453,17 @@ export class Scanner implements ITokenStream {
 		return TOKEN(TokenKind.NumberLiteral, pos, { hasLeftSpacing, value });
 	}
 
+	private tryReadDecimalPoint(hasLeadingDot: boolean): boolean {
+		if (hasLeadingDot) {
+			return true;
+		}
+		if (!this.stream.eof && this.stream.char === '.') {
+			this.stream.next();
+			return true;
+		}
+		return false;
+	}
+
 	private readStringLiteral(hasLeftSpacing: boolean): Token {
 		let value = '';
 		const literalMark = this.stream.char;

test/literals.ts

@@ -58,6 +58,20 @@ describe('literal', () => {
 		eq(res, NUM(0.5));
 	});
 
+	test.concurrent('number (Float with integer zero omitted)', async () => {
+		const res = await exe(`
+		<: .5
+		`);
+		eq(res, NUM(0.5));
+	});
+
+	test.concurrent('number (Float with decimal zero omitted)', async () => {
+		const res = await exe(`
+		<: 5.
+		`);
+		eq(res, NUM(5));
+	});
+
 	test.concurrent('arr (separated by comma)', async () => {
 		const res = await exe(`
 		<: [1, 2, 3]

unreleased/zero-part-ommitable-decimal-literal.md

@@ -0,0 +1,3 @@
+- 数値リテラルの整数部分または小数部分の0を省略できるようになりました。
+    - 整数でない数値リテラルは、整数部分が0の場合、0を省略して記述できるようになりました。
+    - 整数の数値リテラルは、小数部分の0を省略して記述できるようになりました。