Pattern matching¶

{ #feature-pattern-matching }

Stable ID: FEATURE-PATTERN-MATCHING

User-facing summary¶

The system supports sequence-based, kind-based, and structural matching with placeholders and controllable matching criteria.

Related concepts¶

• Matching

Related images¶

• Local image directory: pattern-matching-images/

MISC¶

Scenario: Independent of layout (whitespaces)¶

Scenario: Independent of comments¶

Three cases

1. absent in pattern, present in code
2. present in pattern, absent in code
3. present in pattern, present in code, yet different content

Scenario: Support of placeholders¶

• Placeholders are AST Nodes
• Support of explicit and implicit placeholders

Scenario: Robustness for occurrence of implicit placeholders¶

• in strings, e.g. "$X"
• in comments, e.g., /* $X */.

Scenario: Multiple occurrences of placeholders¶

• Equivalent AST nodes
• Access to all occurrences

Scenario: Multiple assignments of placeholders¶

• E.g., in patterns like $f($$before, $arg, $$after)

Legality of match-patterns¶

For exact matching, we currently accept all patterns. In other words, no illegal match pattern exists.

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1. Match functionality

   1. Elementary matching - "symbols with symbols" - representations of integers, characters, etc.
   2. Basic matching - "code with code" - with(out) comment, with white spaces - note: python is sensitive for indentation
   3. Single placeholder - "pattern with code" - pattern has only one instance of a single placeholder
   4. Multi placeholder - "pattern with code" - pattern has only one instance of a multi placeholder
   5. different placeholders - "pattern with code" with different placeholders (each placeholder occurs only once & only single assignment)
   6. constraint / recurring placeholder - "pattern with code" with single placeholder that occurs multiple times
   7. patterns with multi placeholders that can have multiple assignments
   8. mixed