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Course-info sheet.
What makes a programming-language a language?
- call a function
- loops
- can assign variables?
- loops (or, goto), as part of language?
Which of these functions could we live without? How?
What programming languages have you used / heard of?
- C, Ada, Fortran, Pascal, Rexx, ...
- Smalltalk, Java, C++, C#, ...
- APL; Mathematica; Matlab
- javascript, perl, etc; html ? -- no; data. But, .css.
- postscript:
helloWorld.ps and postscript source
wimpoutBoard.ps and postscript src
- the Unix shell:
cd ~/380/Lectures/
find . -name \*.ps -print
find . -name \*.ps -print | grep -i wimpout
enscript -o foo.ps ; cat foo.ps ; show foo.ps
- a *programmable* calculator.
- MS Word "macros" and mailing-list scripts
- abacus-instructions ?
Families of languages:
procedural; object-oriented; functional; declarative;
scripting(?); math [perhaps 'very-high-level'?]
MS Word, game-level-editors [special-purpose "little languages"]
For example, let's compare two families that share a lot in common:
What is the difference between O.O. and Procedural?
name.substring(3,7) vs substring(name,3,7)
for class Employee,
jo.giveRaise(8.50) vs giveRaise(jo,8.50)
The win comes
(a) through polymorphism (inheritance) --
you can subclass "special" Employees and refine giveRaise;
a procedural approach would have to replace
jo.giveRaise(8.50) with if (jo instanceof SpecialEmployee)
giveSpecialRaise(jo,8.50)
else
giveRaise(jo,8.50)
and these sorts of changes would have to be made
*wherever* the giveRaise method was called.
(b) OO also gives a good way of *organizing* code -- a managerial
tool so everybody knows where to look for certain code.
What makes a program language more *powerful* than another?
("expressive")
Is assembly more powerful than Java?
Java more powerful than assembly?
Church-Turing Thesis:
TM = lambda calculus = RAM = abacus = ...
caveat: phrase in terms of desired *computation*;
while Java doesn't have "change mem location #42BF2" like C does,
C doesn't have "set lever17 of Babbage's Analytic Engine
three notches forward" ... but that's okay,
Knowing a *language* (as opposed to programming) means knowing
Syntax, Semantics, Pragmatics.
Studying languages:
- Syntax -- how to convert to an intermediate form
How to choose to represent exact vs inexact numbers,
how to specify units
e.g. scope of variables, namespaces, ...
- Semantics
e.g. pass-by-ref vs value, ...
- Pragmatics
e.g. What features are helpful to what audiences?
class Account {
int balance;
Account() {
int balance = 100;
}
}
Example of comparing languages: Java vs Scheme:
3+4 (+ 3 4)
3+4*5 (+ 3 (* 4 5))
(3+4)*5 (* (+ 3 4) 5)
Math.sqrt(25) (sqrt 25)
Call a constructor:
new Employee("jo", 4.50)
vs
(make-employee "jo" 4.50)
Access the 3rd element of a list `data`:
data.get(3) (list-ref data 3)
arr[3] (vector-ref arr 3)
- How to call a function:
Java: obj.meth(...) [also with implicit 'this']
class.meth(...)
new ClassName(...)
super(...)
this(...)
a + b (+ a b)
!a (not a)
arr[i] (vector-ref arr i) compare to List.get(i)
arr[i] = ... (vector-set! arr i ...) compare to List.set(i,...)
obj.f (widget-f obj)
obj.f = ... (set-widget-f! obj ...)
- Left with the question: pros/cons of having
operators, as distinct from functions?
- pro: more natural for human readers
- con: a different syntax (harder for compiler-writer; learning?)
- con: requires(?) that those characters are reserved
- con: 37 operators with 14 levels of precedence:
Java precedence table
2.0-1.1
25*(7/25)
- Scheme overview:
- Values: 2, 3.8, #i3.8, "hello", 'orange, >insert-image; true, false
(symbols are like enumerated types)
- Placeholders
(define a 4.2)
(define b 2/3)
(define c (+ a b 17))
(define z 2.7)
(define ufo >insert-image)
- expressions
(/ (+ (- b) (sqrt (- (* b b) (* 4 a c))))
(* 2 a))
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| ©2009, Ian Barland, Radford University Last modified 2009.Feb.08 (Sun) |
Please mail any suggestions (incl. typos, broken links) to iba�rland  rad�ford.edu |
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