Parse tree design

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== Terminology ==
 
== Terminology ==
 
In parsing lingo a ''symbol'' is a name in a grammar.  Each symbol is either a ''terminal'' or a ''non-terminal''.  Non-terminals appear on the left hand side of a grammar production; terminals don't.
 
In parsing lingo a ''symbol'' is a name in a grammar.  Each symbol is either a ''terminal'' or a ''non-terminal''.  Non-terminals appear on the left hand side of a grammar production; terminals don't.
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== Class-Design ==
 
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=== 1st Design ===
 
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[[Image:ParseTree.jpeg]]
 
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That's the first Design that came up in class. It is a [[Composite]] Pattern.
 
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*the addKid()-function in the Terminal class throws an exception
 
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*symbol is of type [[Enum idiom|enum]], which has a representation for every symbol of the grammar.
 
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Problem: [[Beware type switches|Beware of Typeswitch]]
 
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=== 2nd Design ===
 
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[[Image:ParseTreeEnum.jpeg]]
 
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To overcome the [[Beware type switches|Beware of Typeswitch]] problem an enum-hierarchy was added, so that a NonTerminal Symbol cannot have a Terminal Symbol.
 

Revision as of 00:47, 3 August 2009

A context free grammar defines a language, e.g. 

Grammar.gif

A parse tree shows how a sentence in the language is structured according to the grammar. 

Parsetree.gif

Terminology

In parsing lingo a symbol is a name in a grammar. Each symbol is either a terminal or a non-terminal. Non-terminals appear on the left hand side of a grammar production; terminals don't.

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