VisualLangLab - The GUI

Figure-1 below depicts the complete VisualLangLab GUI. The following description details all its features.

The Menu Bar

The Menu Bar (across the top of the GUI) contains the following menus:

• File - the New, Open, Save, SaveAs, and Exit menu-items support the usual operations. When you finish developing and testing a parser (or when work must be suspended temorarily) the parser can be saved to a file by invoking File -> Save or File -> SaveAs. The saved grammar file has a .vll extension, and contains an XML representation of all the data entered into the GUI. A saved grammar can be opened again later for review, testing, or further editing by invoking File -> Open. A saved grammar file can also be loaded by the API from a client program
• View - operations to enable or disable display of additional grammar-tree details, and choose Java look and feel
• Tokens - the New literal, New regex, Edit, Find, and Delete, menu-items perform token management operations. New literal and New regex are used to create new tokens, while Edit is used for editing existing tokens. Find is used to locate parser-rules that use a particular token, and Delete hopefully requires no explanation! The Import and Export items allow token definitions to be imported from or exported to token libraries
• Rules - the New, Rename, Find, Optimize, and Delete menu-items support parser-rule management operations. New rule is used to create new rules, while Rename rule is used for renaming existing rules. Find is used to locate parser-rules that use a particular rule, while Delete does the obvious
• Globals - enables definition of whitespace and comments for the parser
• Test - the Parse input and Parse file items run the parser with input from the Parser Test Input area or a user-specified file respectively. The Tree handler item enables a choice of pretty-printers for the AST (during testing). The Trace all item allows you to start tracing all parsers in one stroke
• Log - the menu-items copy or clear operate on the Parser Log area at the bottom right of the GUI (see Figure-1 above)
• Help - gives access to documentation, sample grammars, and the About page

Starting with version 10.21, the toolbar's dropdown list for rule-names uses certain icons to indicate rule characteristics as in Figure-2 below. A green arrow-icon indicates that the rule includes one or more action-code funtions. The same icon in the magenta color (as for ExprTester in the figure) indicates that that rule has action-code functions designed for testing. A red border around the basic icon (as for factor) indicates the presence of one or more errors in the rule.

Figure-2. The icons of the toolbar's dropdown list

The Tool Bar

The Tool Bar just below the Menu Bar enables quick invocation of commonly used operations:

• File - New (), Open (), Save (), and SaveAs ()operations
• Back button () to display last viewed parser-rule (or grammar-tree)
• Combo box to select parser-rule (or grammar-tree) by name
• Rules - New (), Find (), Optimize (), and Rename () operations
• Tokens - New literal (), New regex (), Edit (), Find (), Import tokens (), and Export tokens () operations
• Test - Parse input (), Parse file (), and Stop parsing () operations
• Log - Copy log (), and Clear log () operations

All toolbar buttons have suggestive tool-tip texts to facilitate use.

The Grammar Tree

The Grammar Tree is the JTree at the top left of the GUI (below the toolbar). It represents the structure of the selected parser-rule (see tool-bar combo-box above). A pop-up context menu is displayed when any node of the grammar-tree is right-clicked. This menu (shown in Figure-1 above) supports grammar-tree editing functions described further in Editing the Grammar Tree.

The AST Area

The Parse Tree (or AST) area is on the right of the grammar-tree (below the toolbar). The structure of the AST produced by the selected grammar-tree node is displayed in this area. The radio buttons (labeled 1, 3, §, and ∞) along the bottom of this area determine the display depth. The values 1 and 3 are literal depths, while § (the section symbol) denotes rule depth, and ∞ (the infinity symbol) displays the complete AST. The variable-depth display is useful for understanding large ASTs.

The format of the displayed information is described in AST and Action Code.

The Action Code Area

The action-code area is the text area at the top right (below the toolbar). This editable area can be used to optionally provide any action-code for the selected grammar-tree node. The action-code must be a Javascript function with one argument. More details and examples can be found in Action Code Design.

The Testing Area

The two text areas along the bottom of the GUI (Parser Test Input and Parser Log) constitute the testing area.

The editable Parser Test Input area on the left is used for providing test input to the parser. Any text typed into this area is read by the parser under development when the Parse input () toolbar button is clicked (or the Test -> Parse input menu item is selected.

The Parser Log area is where any output from the parser run appears. Error messages are printed in red, while normal output is printed in black. When a parser runs to completion successfully, the AST produced is printed out along with some run-time and memory utilization statistics.

Testing within VisualLangLab is described in detail in Testing Parsers.