by
PhilippKutter and
AlfonsoPierantonio. In Journal of Universal
Computer Science, vol. 3, no. 5 (1997), 416--442
Abstract
Montages are a new way of describing all aspects of programming languages formally. Such specifications are intelligible for a broad range of people involved in programming language design and use. In order to enhance readability we combine visual and textual elements to yield specifications similar in structure, length, and complexity to those in common language manuals, but with a formal semantics. The formal semantics is based on Gurevich's Abstract State Machines (formerly called Evolving Algebras).
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Review
Summary
A Montage is a, partially visual, specification of a programming
language construct. The specification consists of a BNF style syntax
definition of the construct, a specification of the control and data
flow through the construct, and a specification of the computation on
the data induced by the construct. Control and data flow are defined
by means of additional edges in the abstract syntax tree. The control
flow edges indicates in which order program points should be visited
during execution. Data flow edges indicate the data dependencies
between nodes. The flow information can be specified using a visual
language. The following picture shows the control and data flow of
the while construct:
Computations are defined by functions applied to the values
of previously computed nodes. Control flow is determined by actions
which manipulate the abstract program counter
CurrentTask
. Control
flow can be conditional on data values.
A Montage is translated to rules for an
AbstractStateMachine?. These
rules define how the abstract program counter and the contents of the
store are changed by the computations of the tokens. The implicit
parallelism of the rules is tamed by annotating program points with
flags that indicate whether it has been executed already.
Questions/Remarks
- Could control flow not be deduced from the data dependencies? First perform the computations corresponding to those nodes from which data is needed.
- The EvaluationStrategy? is determined by the specification of control flow. How could one model different evaluation strategies for the same language? In other words, tying together all semantic aspects of a language constructs prevents reuse of some aspect.
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EelcoVisser - 23 Dec 2001
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