[英]Parse Tree Of Context Free Grammar
I'm trying to figure out how to do parse trees correctly to show whether a grammar is ambiguous or not. 我试图弄清楚如何正确地解析树以显示语法是否模棱两可。
my grammar is S -> xSy | 我的语法是S-> xSy | ySx |
ySx | SS |
SS | e
Ë
any help would be great. 任何帮助都会很棒。 thanks in advance
提前致谢
below is my crack at it... 下面是我的裂缝...
S
/ \
/ \
x y
/ \ / \
x x y y
As a hint, pretty much any grammar with a production of the form 提示:几乎所有带有形式的语法
S → SS
S→SS
will be ambiguous, because if you want to produce three S nonterminals you can do so in two ways: 这将是模棱两可的,因为如果您想产生三个S非末端,则可以通过两种方式进行:
S S
/ \ / \
S S S S
/ \ / \
S S S S
Assuming those S's can actually produce strings of terminals, these two "gadgets" can be put into the parse tree to derive the same string in two different ways. 假设那些S实际上可以产生终端字符串,则可以将这两个“小工具”放入解析树中,以两种不同的方式派生相同的字符串。
Hope this helps! 希望这可以帮助!
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