Introduction to Programming Languages: Key Concepts and Structures

1. CSE3302Programming Languages(more notes) Dr. Carter Tiernan Programming Languages

2. Return to Simplicity • Attempts to extend Algol included: • PL /I • very large • intersection of FORTRAN, COBOL, and Algol • “Swiss army knife” approach • Extensible languages • Kernal: application independent • Ex: operator extensions & syntax macros • Inefficient; hard to debug Programming Languages

3. Pascal • Niklaus Wirth designed successor languages to Algol • Goal was to compete with FORTRAN and keep the benefits of Algol • Explicit goals • Suitable for teaching programming • Reliable, efficient implementation Programming Languages

4. Pascal Structure • Syntax is Algol-like • Uses reserved words • New structures added • Name • Data • Control Programming Languages

5. Data Structures • Primitives • Real, integer, boolean from Algol • Characters : type char • Enumeration types • Replaces integer codes to represent lists • Limits range of values explicitly • Keeps types unique and separate • Defined as a binding construct • Only allows meaningful operations • Efficient implementation Programming Languages

6. Data Structures, continued • Subrange types • Security and efficiency • Set types • Mathematical application • Efficient • Set operations defined - implemented with bit operations Programming Languages

7. Arrays • Generalized index types (integer subranges) • Allowable element types - any other Pascal base type including other arrays, etc. • No multi dimensional arrays BUT can have an array whose element type is array and “syntactic sugar” allows appearance of multi-dim arrays • Restrictions on Pascal arrays • Static bounds : determinable at compile time • Dimensions are part of array type • Feature interaction problem with bounds Programming Languages

8. Records • Aggregate heterogeneous data • Components can be primitive types or complex data types including records and arrays • Component selection within a record is done with dot notation • with statement opens a record for accessing multiple fields within the block of the with Programming Languages

9. Arrays vs. Records Programming Languages

10. Variant Records • Groups different fields according to a status value • The status value is called the tag field • Creates a loophole related to type because variant fields do not have to be initialized and previous values of different type may be accessible Programming Languages

11. Data types (cont.) • Pascal structures allow efficient information storage • Pascal has pointers • Pointers have data types to support strong typing in Pascal • Pointer base types can be any other type • Initially type equivalence was not clearly defined • Structural, Name (simpler and safer) • Subrange equivalence within Name eq Programming Languages

12. Name Structures • Bindings • Constant • Type • Variable • Procedure and function • Implicit enumeration • Label Programming Languages

13. Name Structures • Constants abstract out dependencies • Constants cannot be described by an expression • Expressions cannot be used in variable or type declarations Programming Languages

14. Name Struct Constructors • Records • Procedures • Much like Algol in format and scope • Order of declarations was important for one-pass compilation • Reverses top-down order • No way to define mutually recursive procs • forward declaration (like C prototype decl) • Group order important also Programming Languages

15. Control Structures • More structures than Algol but simpler • I/O routines provided • Structured control is supported • One entry, one exit • Supports recursion • Has a goto to facilitate adoption Programming Languages

16. Structures • for • Austere & even simpler than FORTRAN DO • while / do • Condition at beginning • repeat / until • Condition at end • case • Labeled cases Programming Languages

17. Parameters • Pass by reference • Pass by value • Pass by constant • Input parameter treated as a constant inside called routine • Compiler can either copy or pass address of parameter • Left loophole similar to aliasing problem Programming Languages

18. Procedural parameters • Can pass procedures and functions as parameters • Originally, formal specification gave procedure name and return type but not parameters of procedure being passed • Standard required parameters to be specified also Programming Languages

19. Pascal • Excellent teaching language • Suitable for “real” programming • Usage goes beyond original intent Programming Languages

20. Other Languages • PL /I extensions • BCPL - Cambridge Plus London • B - BCPL based & used in 1st Unix (8k PDP-7) • C - successor of ‘B’ by Dennis Ritchie • Used to rewrite Unix kernel • Characteristics of 1st, 2nd, and 3rd gen languages • PL /I extensions • BCPL - Cambridge Plus London • B - BCPL based & used in 1st Unix (8k PDP-7) • C - successor of ‘B’ by Dennis Ritchie • Used to rewrite Unix kernel • Characteristics of 1st, 2nd, and 3rd gen languages Programming Languages

21. Third Generation Languages 3rd • Simplicity and efficiency • Data structures support applications • Support nesting • User definition • Pointers • Name structures have bindings for new types • Control structures are simplified and efficient • Case Programming Languages