Language Interpreters in Maude

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Language Interpreters in Maude

• Mark Hills
• UIUC SIGPLAN
• April 11, 2005

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Overview

• Language specification
• Benefits
• What to watch out for
• Goal give you a sense of how Maude works,
  without getting bogged down in (too many) details

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Language specification

• Goal provide a formal specification of a
  language
• Should be a mathematical model of how the
  language works
• Benefit should be executable should be able to
  run programs in this model

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General process

• Specify syntax
• Create execution environment
• Specify semantics

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Specify syntax

• Syntax specified in mixfix notation
• Similar to BNF productions
• Can specify operator precedence and associativity

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Example 1 Basic constructs
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Example 2 Functional constructs
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Example 3 Lambda calculus
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Create execution environment

• Maude does not provide a default execution
  environment for us we need to model it
• Generally need an environment, a store, and some
  additional state information
• Can add constructs to represent threads, locks,
  etc

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Example 1 A basic environment
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Example 2 The store
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Example 3 Threads
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Specify semantics

• With syntax and an execution environment, need to
  specify semantics of the language features
• Semantics have an operational feel based on
  equational reasoning
• Semantics generally change the current expression
  and the state

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Example 1 Basic math
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Example 2 Loops
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Example 3 Functions
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Benefits

• The model is mathematical it is a formal model
  that we can reason about
• The model is executable we can actually run
  programs using this model
• The model is fast programs run in a reasonable
  amount of time
• The model is detailed we make no assumptions,
  so we understand how it works

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What to watch out for

• Parsing is tricky probably the biggest weakness
  to this approach
• Closed world assumption cannot take input or
  generate output from the outside world
• Performance sometimes does matter a cumbersome
  formal model will be slow, and probably can be
  streamlined

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Questions?