feat: add nil token to allow nil permission expressions

TODO: add more tests to make sure this doesn't break anything

pkg/dsl/lexer/lexer.go

@@ -147,9 +147,13 @@ func (l *Lexer) NextToken() (tok token.Token) {
 		if isLetter(l.ch) {
 			tok.PositionInfo = positionInfo(l.linePosition, l.columnPosition)
 			tok.Literal = l.lexIdent()
-			if tok.Literal == "true" || tok.Literal == "false" {
+			switch tok.Literal {
+			case "true", "false":
 				tok.Type = token.BOOLEAN
 				return
+			case "nil":
+				tok.Type = token.NIL
+				return
 			}
 			tok.Type = token.LookupKeywords(tok.Literal)
 			return

pkg/dsl/lexer/lexer_test.go

@@ -980,5 +980,97 @@ rule check_ip_address(ip_addresses string[]) {
 				Expect(index + lexeme.Literal).Should(Equal(index + tt.expectedLiteral))
 			}
 		})
+
+		It("Case 10", func() {
+			str := `
+entity user {}
+
+entity organization {
+	relation admin @user
+    relation member @user
+
+	action create_repository = nil
+	action delete = nil
+}
+
+`
+
+			tests := []struct {
+				expectedType    token.Type
+				expectedLiteral string
+			}{
+				{token.NEWLINE, "\n"},
+				{token.ENTITY, "entity"},
+				{token.SPACE, " "},
+				{token.IDENT, "user"},
+				{token.SPACE, " "},
+				{token.LCB, "{"},
+				{token.RCB, "}"},
+				{token.NEWLINE, "\n"},
+				{token.NEWLINE, "\n"},
+				// --
+				{token.ENTITY, "entity"},
+				{token.SPACE, " "},
+				{token.IDENT, "organization"},
+				{token.SPACE, " "},
+				{token.LCB, "{"},
+				{token.NEWLINE, "\n"},
+				// --
+				{token.TAB, "\t"},
+				{token.RELATION, "relation"},
+				{token.SPACE, " "},
+				{token.IDENT, "admin"},
+				{token.SPACE, " "},
+				{token.SIGN, "@"},
+				{token.IDENT, "user"},
+				{token.NEWLINE, "\n"},
+				// --
+				{token.SPACE, " "},
+				{token.SPACE, " "},
+				{token.SPACE, " "},
+				{token.SPACE, " "},
+				{token.RELATION, "relation"},
+				{token.SPACE, " "},
+				{token.IDENT, "member"},
+				{token.SPACE, " "},
+				{token.SIGN, "@"},
+				{token.IDENT, "user"},
+				{token.NEWLINE, "\n"},
+				{token.NEWLINE, "\n"},
+				// --
+				{token.TAB, "\t"},
+				{token.PERMISSION, "action"},
+				{token.SPACE, " "},
+				{token.IDENT, "create_repository"},
+				{token.SPACE, " "},
+				{token.ASSIGN, "="},
+				{token.SPACE, " "},
+				{token.NIL, "nil"},
+				{token.NEWLINE, "\n"},
+				// --
+				{token.TAB, "\t"},
+				{token.PERMISSION, "action"},
+				{token.SPACE, " "},
+				{token.IDENT, "delete"},
+				{token.SPACE, " "},
+				{token.ASSIGN, "="},
+				{token.SPACE, " "},
+				{token.NIL, "nil"},
+				{token.NEWLINE, "\n"},
+				{token.RCB, "}"},
+				{token.NEWLINE, "\n"},
+				{token.NEWLINE, "\n"},
+				// --
+			}
+
+			l := NewLexer(str)
+
+			for i, tt := range tests {
+				lexeme := l.NextToken()
+				index := strconv.Itoa(i) + ": "
+				Expect(index + lexeme.Type.String()).Should(Equal(index + tt.expectedType.String()))
+				Expect(index + lexeme.Literal).Should(Equal(index + tt.expectedLiteral))
+			}
+		})
 	})
 })

pkg/dsl/parser/parser.go

@@ -64,9 +64,10 @@ func NewParser(str string) (p *Parser) {
 		references: ast.NewReferences(), // initialize an empty map for relational references
 	}
 
-	// register prefix parsing functions for token types IDENT and NOT
+	// register prefix parsing functions for token types IDENT and NIL
 	p.prefixParseFns = make(map[token.Type]prefixParseFn)  // initialize an empty map for prefix parsing functions
 	p.registerPrefix(token.IDENT, p.parseIdentifierOrCall) // associate the parseIdentifier function with the IDENT token type
+	p.registerPrefix(token.NIL, p.parseIdentifierOrCall)
 
 	// register infix parsing functions for token types AND, OR, NOT
 	p.infixParseFunc = make(map[token.Type]infixParseFn) // initialize an empty map for infix parsing functions

pkg/dsl/parser/parser_test.go

@@ -1041,5 +1041,22 @@ rule confidentiality_level_low(confidentiality_level double) {
 			// Ensure the error message contains the expected string
 			Expect(err.Error()).Should(ContainSubstring("7:15:expected token to be RELATION, PERMISSION, ATTRIBUTE, got OR instead"))
 		})
+
+		It("Case 30 - Nil Permission", func() {
+			pr := NewParser(`
+			entity account {
+    			relation owner @user
+    			relation admin @user
+
+				action check_balance = nil
+
+    			permission withdraw = nil 
+			}
+			`)
+
+			_, err := pr.Parse()
+			// Ensure an error is not returned
+			Expect(err).ShouldNot(HaveOccurred())
+		})
 	})
 })

pkg/dsl/token/token.go

@@ -76,6 +76,7 @@ const (
 	INTEGER = "INTEGER"
 	DOUBLE  = "DOUBLE"
 	BOOLEAN = "BOOLEAN"
+	NIL     = "NIL"
 
 	/*
 		Symbols