Language Design Principles

1
Language Design Principles
2
Criteria ?

• It is very difficult to offer criteria for good
  programming language design
• Criteria for good programming language design
  often conflict each other
• Programming languages have been successes or
  failures for many different reasons
• Programming language design is a goal-orientd
  activity

3
Efficiency

• Efficiency of compiler construction
  implementability
• Efficiency of compiler execution simplicity,
  reliability
• Efficiency of program construction writability,
  expressiveness
• Efficiency of program execution optimizability
• Efficiency of program modification readability,
  maintainability

4
Regularity

• Regularity is a measure of how well a language
  integrates its features, so that there are no
  unusual restrictions, interactions, or behavior
• Regularity can be placed in subcategories
  Generality, Orthogonality, Uniformity

5
Generality

• Do constructs have as few restrictions as
  possible?
• In Pascal, functions can be passed as parameters,
  but there are no function variables. C lacks
  nested functions. Scheme and ML have completely
  general functions
• Fortran can pass variable-length array
  parameters, but cannot define variable-length
  array variables

6
Orthogonality

• Can constructs be combined in any meaningful way?
• In Pascal, functions can return only scalar or
  pointer types as values. In C and C, values of
  all types, except array types, can be returned.
  In Ada and functional languages, values of all
  types can be returned

7
Uniformity

• Do similar things look the same, and do different
  things look different?
• In C, a semicolon is necessary after a class
  definition but forbidden after a function
  definition
• In Pascal, returned values from functions look
  like assignments

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Other Criteria

• Simplicity make things as simple as possible,
  but not simpler. (Pascal, C)
• Expressiveness make it possible to express
  conceptual abstractions directly and simply.
  (Scheme, Simula67)
• Extensibility allow the programmer to extend the
  language in various ways. (Scheme, C)
• Security programs cannot do unexpected damage.
  (Java)

9
Other Criteria

• Preciseness having a definition that can answer
  programmers and implementors questions. (Most
  languages today, but only one has a mathematical
  definition ML)
• Machine-independence should run the same on any
  machine. (Java)
• Consistent with accepted notations. (Most
  languages today, but not APL)
• Restrictability a programmer can program
  effectively in a subset of the full language.
  (C avoids runtime penalties)

10
C A Case Study

• Thanks to Bjarne Stroustrup, C is not only a
  great success story, but also the best-documented
  language development effort in history
• 1997 The C Programming Language, 3rd Edition
  (Addison-Wesley).
• 1994 The Design and Evolution of C
  (Addison-Wesley).
• 1993 A History of C 1979-1991, SIGPLAN Notices
  28(3).