LL(1) Parser Applet: Output Windows
Last Update Time-stamp: "97/06/28 17:16:42 umrigar"
The LL(1) parser displays its output in three windows:
Parse Tree Window
The top window displays the parse tree as it is being constructed. Nodes
which are still on the parse stack
are shown in green (tracing the green nodes from the bottom to the top gives
the contents of the stack). When a node is removed from the parse stack,
it's color is changed to red. As the parser is stepped, the window will
always display the current node of interest which is highlighted in yellow.
LL(1) Parse Table Window
This shows the LL(1) parse table.
The table contains rule numbers. When a nonterminal is being predicted, the
appropriate row (indexed by nonterminal) and column (indexed by terminal)
are highlighted to show the predicted rule. Since a LL(1) parse table does
not need any rows indexed by terminal symbols, no row in the table is
highlighted when a terminal is being predicted.
Trace Window
This window shows the trace history in the format used in classical compiler
texts. Each trace line consists of the stack (in green) followed by the
input (in black) which is yet to be processed. The current lookahead token
is always the first token in the unexpended input. The stack is the reverse
of what remains to be seen in the current sentential form. The stack
contents correspond to the green nodes in the parse tree.
Each window displays a brief description of itself for a short period
after the mouse pointer enters it.
Feedback: Please email any feedback to zdu@acm.org.
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