Build.bat

1
Build.bat

• wicont -c xcode escape ebcdic
• wicont -c parsell1 readll1 semstk eulerscn
• wicont -fs euler eulersem eulerint parsell1
  readll1 semstk eulerscn

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T0exp.eul

• begin new a new y new z ( declare vbls )
• a lt- list 2 ( make 'a' a list )
• y lt- 2 ( assign y a value of 2 )
• a1 lt- y 4 ( a1 2 4 )
• out a1 ( display 2 4 )
• a2 lt- 2 ( assign value to a2 )
• out a1 a2 ( display 16 2 )
• ( NOTE NO semicolon on next to last line of
  program )
• end

3
Nonimperative Programming Models

• Imperative - focus on how the computer should do
  its work
• C, Pascal, Fortran
• Declarative - focus on what the computer should
  do
• functional - modeled after lambda calculus
• Lisp

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Functional and Logic Languages

• Functional languages
• make heavy use of subroutines
• Logic languages
• formal specifications and theorem proving

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Historical Origins

• imperative and functional models
• Turing, Church, Kleene, Post in the 1930s
• Turing machine computes in an imperative way
• Church's model of computing is called the lambda
  calculus based on the notion of parameterized
  expressions
• Logic programming is tied to the notion of
  constructive proofs

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Programmers View

• imperative programmer
• To compute the gcd of a and b, check to see if a
  and b are equal. If so, print one of them and
  stop. Otherwise, replace the larger one by their
  difference and repeat.
• functional programmer
• The gcd of a and b is defined to be a when a and
  b are equal, and to be the gcd of c and d when a
  and b are unequal, where c is the smaller of a
  and b, and d is their difference.

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Programmers ViewLogic Programmer

• The proposition gcd (a, b, g) is true if
• (1) a, b, and g are all equal, or
• (2) there exist numbers c and d such that c is
  the minimum of a and b (i.e., min (a, b, c) is
  true), d is their difference (i.e., minus (a, b,
  d) is true), and gcd(c, d, g) is true. To compute
  the gcd of a given pair of numbers, search for a
  number g (and various numbers c and d) for which
  these two rules allow one to prove that gcd (a,
  b, g) is true.

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Characteristics of Function-Oriented Programming
Languages

• emphasis on the use of pure functions
• minimal use of assignment operations
• high level of abstraction
• lack of dependence on assignment operations
  allows function-oriented programs to be evaluated
  in many different orders
• absence of assignment operations makes
  function-oriented programs much more amenable to
  mathematical proof and analysis than are
  imperative programs

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Functional Languages

• First-class function values and higher-order
  functions
• Extensive polymorphism
• List types and operators
• Recursion
• Structured function returns
• Constructors (aggregates) for structured objects
• Garbage collection

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Overview of Scheme

• runs a "read-eval-print" loop
• ( 3 4) prints 7
• 7 prints 7
• (( 3 4))
• '( 3 4) evaluates to ( 3 4)
• (if (gt a 0) ( 2 3) ( 2 "foo") )
• (char? x) is x a character?
• (string? x) is x a string?
• (number? x) is x a number?
• (list? x) is x a (proper) list?