Silver - an Attribute Grammar
Specification Language
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Silver is an attribute grammar specification language that we have
developed to investigate highly-modular attribute grammar-based
language specifications.
Our LDTA 2007 paper "Silver: an Extensible Attribute Grammar System"
is available here
Silver version 0.1 supports many extensions to D. E. Knuth's
original specification of attribute grammars. This include:
Forwarding: In our paper
"Forwarding
in Attribute Grammars for Modular Language Design" we show how the
notion of forwarding is integrated into attribute grammars. This
feature is very useful in defining modular language extensions because
it allows some aspects of a new constructs semantics to be specified
implicitly via a translation to the host language. Semantics can be
explicitly specified using traditional attribute definitions.
Higher-order attributes as defined by Vogt and
a form of reference attributes that are similar in spirit to Hedin's.
Collections as specified by Boyland are also supported
in Silver. Pattern matching over syntax trees. This is similar to
what is found in ML and Haskell. Syntax trees correspond to
algebraic data type values and productions correspond to value
constructors.
Polymorphic lists are also included and are similar
to what is found in ML and Haskell. Silver version 0.2 will
support parametric polymorphism in general.
Silver evaluates attributes by translating Silver specifications to
Haskell. As a lazy functional language, Haskell is well suited to
this sort of task. The translator to Haskell is implemented in Silver
and thus we have utilized the extensible nature of Silver
specification to extend Silver itself.
Silver has been tested on ubuntu linux for both 32 and 64 bit systems.
It should run on any *nix system that has the Glasgow Haskell
Compiler. Please see the downloads
page for source specification, executables, installation instructions
and demos. More details are available in the User
Manual.
Parser Generators
The downloads include source (and for Copper, executables) for
different versions of Silver that use different parser generators.
The first is silver.happy - it uses Haskell-based alex and happy, the
Haskell versions of lex and yacc. The second is silver.copper - it is
a parser and scanner generator that we have developed that uses
"context aware scanning". This technique is particularly useful in
extensible languages and is described in our GPCE 2007 paper Context-Aware
Scanning for Parsing Extensible Languages. Some information on
specifications in Silver of Copper grammars can be found here: Copper.
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