Add value-returning match expressions

internal/lang/parser.go

@@ -793,6 +793,68 @@ func (p *parser) parseMatch() (Stmt, error) {
 	return MatchStmt{Value: value, Cases: cases}, nil
 }
 
+func (p *parser) parseMatchExpr() (Expr, error) {
+	if _, err := p.expect(tokenLParen, "expected '(' after match"); err != nil {
+		return nil, err
+	}
+	value, err := p.parseExpr(0)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := p.expect(tokenRParen, "expected ')' after match value"); err != nil {
+		return nil, err
+	}
+	if _, err := p.expect(tokenLBrace, "expected '{' after match value"); err != nil {
+		return nil, err
+	}
+	var cases []MatchExprCase
+	for !p.check(tokenRBrace) && !p.check(tokenEOF) {
+		enumName, err := p.expect(tokenIdent, "expected enum name in match case")
+		if err != nil {
+			return nil, err
+		}
+		if _, err := p.expect(tokenDoubleColon, "expected '::' in match case"); err != nil {
+			return nil, err
+		}
+		variant, err := p.expect(tokenIdent, "expected variant name")
+		if err != nil {
+			return nil, err
+		}
+		var bindings []string
+		if p.match(tokenLParen) {
+			if !p.check(tokenRParen) {
+				for {
+					binding, err := p.expect(tokenIdent, "expected variant binding")
+					if err != nil {
+						return nil, err
+					}
+					bindings = append(bindings, binding.lexeme)
+					if !p.match(tokenComma) {
+						break
+					}
+				}
+			}
+			if _, err := p.expect(tokenRParen, "expected ')' after variant bindings"); err != nil {
+				return nil, err
+			}
+		}
+		if _, err := p.expect(tokenArrow, "expected '->' after match pattern"); err != nil {
+			return nil, err
+		}
+		result, err := p.parseExpr(0)
+		if err != nil {
+			return nil, err
+		}
+		cases = append(cases, MatchExprCase{EnumName: enumName.lexeme, VariantName: variant.lexeme, Bindings: bindings, Value: result})
+		p.match(tokenComma)
+		p.match(tokenSemicolon)
+	}
+	if _, err := p.expect(tokenRBrace, "expected '}' after match"); err != nil {
+		return nil, err
+	}
+	return MatchExpr{Value: value, Cases: cases}, nil
+}
+
 func (p *parser) parseSelect() (Stmt, error) {
 	if _, err := p.expect(tokenLBrace, "expected '{' after select"); err != nil {
 		return nil, err
@@ -1016,6 +1078,8 @@ func (p *parser) parsePrefix() (Expr, error) {
 		return p.parsePostfix(expr)
 	case tokenLBrace:
 		return p.parseLambdaExpr()
+	case tokenMatch:
+		return p.parseMatchExpr()
 	case tokenBang, tokenMinus, tokenAmp, tokenStar:
 		value, err := p.parseExpr(7)
 		if err != nil {