LL(1) Parser Generator

An LL parser or Left-to-right, leftmost derivation parser, is a top down parser for a restricted context free language. This visualizer shows an LL(1) parser which has one lookahead in form FIRST and FOLLOW sets. The FIRST set of a nonterminal NT, FIRST(NT), is the set of terminals that can be the first element of any string derived from NT. FOLLOW(NT) is a set of terminals that can appear immediately to the right of NT in any derivation. LL(1) grammars must not have certain conflicts, such as FIRST/FIRST conflicts, left recursion, and FIRST/FOLLOW conflicts.

LL(1) Parser

Grammar Input

Epsilon is denoted with %
Grammar must have S as the start symbol
Rules are in form nonterminal > terminals/nonterminals ('>' can be used as a token)
Each token in a rule must be separated by a space
$ is reserved as EOF

Any conflicts in the grammar will show up red on the table
Click 'Set' to start/reset parsing
The 'Next step' button will build the next production in the parse tree
The center button on the Dpad will extend the view port downwards for the tree
The rest of the buttons move the tree around in the view port
Nodes in the tree can be collapsed when clicked

Tables

First and Follow Sets
NonTerminals	First	Follow
S	(, num, ident	$
EXPR	(, num, ident	$, )
EXPR'	+, -, %	$, )
TERM	(, num, ident	$, +, -, )
TERM'	*, /, %	$, +, -, )
FACTOR	(, num, ident	$, +, -, *, /, )

Parse Table
-	+	-	*	/	(	)	num	ident	$
S	-	-	-	-	EXPR	-	EXPR	EXPR	-
EXPR	-	-	-	-	TERM EXPR'	-	TERM EXPR'	TERM EXPR'	-
EXPR'	+ TERM EXPR'	- TERM EXPR'	-	-	-	%	-	-	%
TERM	-	-	-	-	FACTOR TERM'	-	FACTOR TERM'	FACTOR TERM'	-
TERM'	%	%	* FACTOR TERM'	/ FACTOR TERM'	-	%	-	-	%
FACTOR	-	-	-	-	( EXPR )	-	num	ident	-

Parse Input

Stack

Rest of input

Rule used