The first programming project involves writing a program that parses, using recursive descent, a GUI
definition language defined in an input file and generates the GUI that it defines. The grammar for this
language is defined below:
Window STRING '(' NUMBER ',' NUMBER ')' layout widgets End '.'
Layout layout_type ':'
Grid '(' NUMBER ',' NUMBER [',' NUMBER ',' NUMBER] ')'
widget widgets |
Button STRING ';' |
Group radio_buttons End ';' |
Label STRING ';' |
Panel layout widgets End ';' |
Textfield NUMBER ';'
radio_button radio_buttons |
Radio STRING ';'
In the above grammar, the red symbols are nonterminals, the blue symbols are tokens and the black
punctuation symbols are BNF metasymbols. Among the tokens those in title case are keywords. The
character literals are punctuation tokens.
Below is an explanation of the meaning of some of the symbols in the above productions that should
help you understand the actions that are to be performed when each of the productions is parsed:
In the window production the string is the name that is to appear in the top border of the
window and the two numbers are the width and height of the window
In the production for layout_type that define the grid layout, the first two numbers represent
the number of rows and columns, and the optional next two the horizontal and vertical gaps
In the production for widget that defines a button, the string is the name of the button
In the production for widget that defines a label, the string is text that is to be placed in the label
In the production for widget that defines a text field, the number is the width of the text field
In the production for radio_button, the string is the label of the button
You parser should properly handle the fact that panels can be nested in other panels. Recursive
productions must be implemented using recursion. Syntactically incorrect input files should detect and
report the first error.
Below is an example of an input file:
Window "Calculator" (200, 200) Layout Flow:
Panel Layout Grid(4, 3, 5, 5):