深入理解運算原理｜從簡單的機器到無所不能的程式

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現在我們有了解析正規運算式所需要的所有部分，接著就將它轉換成抽象語法樹，並使

用它來匹配字串：

>> require 'treetop'

=> true

>> Treetop.load('pattern')

=> PatternParser

>> parse_tree = PatternParser.new.parse('(a(|b))*')

=> Sy ntaxNode+Repeat1+Repeat0 offset=0, "(a(|b))*" (to_ast,brackets):

SyntaxNode+Brackets1+Brackets0 offset=0, "(a(|b))" (to_ast,choose):

SyntaxNode offset=0, "("

SyntaxNode+Concatenate1+Concatenate0 offset=1, "a(|b)" (to_ast,first,rest):

SyntaxNode+Literal0 offset=1, "a" (to_ast)

SyntaxNode+Brackets1+Brackets0 offset=2, "(|b)" (to_ast,choose):

SyntaxNode offset=2, "("

Sy ntaxNode+Choose1+Choose0 offset=3, "|b" (to_ast,first,rest): SyntaxNode+Empty0

offset=3, "" (to_ast) ...