23 lines
1.2 KiB
Markdown
23 lines
1.2 KiB
Markdown
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# Parsing dev documentation
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Parsing happens in a structured manner and happens in different phases.
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This document explains these phases.
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## 1) Expression gets parsed into a tokenlist (tokenized)
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A string gets parsed from left to right and gets converted into a list of tokens.
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The tokens are available in `tokens.py`.
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## 2) Tokenlist get transformed to expression tree (AST)
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This is the parsing of the token list. This parsing will result in an Abstract Syntax Tree (AST).
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The different node types are available in `ast_nodes.py`. The AST is a representation that has all
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the information that is in the expression but its tree form allows processing it in a structured manner.
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## 3) The AST gets validated (full semantic correctness)
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The AST is used for validation. The paths and attributes are validated to be correct. At the end of the
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validation all the values will be resolved.
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## 4) Update Expression gets executed using the validated AST
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Finally the AST is used to execute the update expression. There should be no reason for this step to fail
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since validation has completed. Due to this we have the update expressions behaving atomically (i.e. all the
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actions of the update expresion are performed or none of them are performed).
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