Name Rascal/Expressions/ConcreteSyntax

Synopsis Concrete syntax is a notation for patterns that match parse trees and expressions that generate them.

Syntax

1. (Nonterminal) `sentence`

2. `sentence`

where each sentence is a string over the language generated from Nonterminal. This language is extended in the following way. Each non-terminal reachable X from Non-terminal has an added alternative to allow nested Rascal Patterns inside of concrete syntax fragments:

• syntax X = "<" Pattern p ">";

Description A concrete syntax fragment allows the programmer to write patterns and expressions in the language that is currently analyzed, transformed or generated. The ConcreteSyntax feature is derived from SyntaxDefinitions. For any non-terminal defined in a SyntaxDefinition, you may use ConcreteSyntax to match or generate its parse trees.

Benefits

• Easy notation for complex structures

Pitfalls

• Since Rascal currently has no type-checker, the disambiguation of concrete syntax fragments is done heuristically which may lead to surprises.
• The disambiguation of embedded concrete syntax fragments may change in the near future.

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