---++ Name

ambtracker -- display the productions in a parse tree causing ambiguities

---++ Description

Compared to [[VisualizeAmbiguities][visamb]] =ambtracker= offers an alternative visualization of ambiguities in a parse tree. =ambtracker= just displays the productions causing the ambiguity and not how these productions are applied to the actual input. The location (row and column) in the input where an ambiguity is caused is also displayed for easy reference.

Consider the syntax definition that is used to illustrate [[VisualizeAmbiguities][visamb]].
<verbatim>
  definition
  module Main
  exports
	 sorts Exp
	 lexical syntax
		[\ \t\n] -> LAYOUT
	 context-free syntax
		"id"	 -> Exp
		Exp Exp -> Exp
</verbatim>

From this syntax definition an SGLR parse table can be generated:
<verbatim>
  sdf2table -i Exp.sdf -o Exp.tbl
</verbatim>

The ambiguities of the phrase =id id id= can be shown with:
<verbatim>
  echo "id id id" | sglr -2 -p Exp.tbl | ambtracker
</verbatim>

the output of this command is:
<verbatim>
  1 ambiguity cluster:

  [1/1] at (1:0):
	 Exp  Exp -> Exp
	 Exp  Exp -> Exp
</verbatim>