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Concrete Syntax

rascal-0.40.17

Synopsis​

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

Syntax​

`(Nonterminal) `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 = "<" Type Var ">";`

Description​

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

Benefits​

  • Easy notation for complex structures
  • The leading Nonterminal always scopes the right parser to run.
  • Source-to-source transformations are easy with concrete syntax patterns.