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lect01a
images as values
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?
* postscript
Example: enscript -o foo.ps ; cat foo.ps ; show foo.ps
Example: cat wimpoutBoard.ps ; show wimpoutBoard.ps
- C, Ada, Fortran, Pascal, Rexx, ...
- Smalltalk, Java, C++, C#, ...
- APL; Mathematica; Matlab
- javascript, perl, etc; html ? -- no; data. But, .css.
- sh/csh, .bat, applescript; scriptable photoshop?
Example: cd ~/Unix
find \*.ps
find \*.ps | grep -i wimpout
- a *programmable* calculator.
* MS Word "macros" and mailing-list scripts
- abacus-instructions ?
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,
========
Example of comparing languages:
In Java / 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 in Scheme?
syntax:
( ~funcname~ ~expr~ ~expr~ ... )
How to call a function in Java?
syntax: ~obj~.~methname~( ~expr~, ~expr~, ...)
~methname~( ~expr~, ~expr~, ...)
~class~.~methname~( ~expr~, ~expr~, ...)
new ~className~( ~expr~, ~expr~, ...)
~expr~ ~op~ ~expr~
~op~ ~expr~
~array~[~expr~]
~array~[~expr~] = ...
Course-info sheet.
Knowing a *language* (as opposed to programming) means knowing
Syntax, Semantics, Pragmatics.
Studying languages:
- Syntax -- how to convert to an intermediate form
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;
}
}
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