19 lines
1.1 KiB
Text
19 lines
1.1 KiB
Text
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Languages can be split into two components, their *syntax* and their
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*semantics*. It's your understanding of English syntax that tells you
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the stream of words "Sleep furiously green ideas colorless" is not a
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valid sentence. Semantics is deeper. Even if we rearrange the above
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sentence to be "Colorless green ideas sleep furiously", which is
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syntactically correct, it remains nonsensical on a semantic
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level. With Treetop, you'll be dealing with languages that are much
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simpler than English, but these basic concepts apply. Your programs
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will need to address both the syntax and the semantics of the
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languages they interpret.
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Treetop equips you with powerful tools for each of these two aspects
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of interpreter writing. You'll describe the syntax of your language
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with a *parsing expression grammar*. From this description, Treetop
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will generate a Ruby parser that transforms streams of characters
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written into your language into *abstract syntax trees* representing
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their structure. You'll then describe the semantics of your language
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in Ruby by defining methods on the syntax trees the parser generates.
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