Transcript COBOL, LISP, and Pythonx

COBOL, LISP, and Python
Joseph Hoeppner
COBOL Background

Released in 1959

Grace Hopper
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Industry, universities, and government collaboration
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Cold War pressures
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80% of business transactions
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65% of all code is in COBOL
COBOL – Why?

Software Lifecycle

Cheaper to maintain
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Y2K
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Self-documenting code
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Verbose
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“IF a < b AND > c …”
Divisions
COBOL – Why?
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Divisions
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Identification Division
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Environment Division
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Data Division
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Procedure Division
COBOL – Data Division
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Data Division
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Pictures
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9 = digit
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X = any character
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A = alphabetic character
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V = decimal point position
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S = sign
Repeats
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PIC 9 (4) = 9999
COBOL – Groups and Elementary data
COBOL


Reliability
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Stood test of time
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Has “ALTER X TO PROCEED TO Y” (a negative)
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Uses GOTO statements (a negative)
Today
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Cross platform: OpenCOBOL C translation
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IDEs (Net Express)
COBOL - Summary

Readability

Writability

Reliability
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Portability
LISP
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LISt Processing
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List-based language
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2nd High-level language
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1958 – John McCarthy for MIT
LISP - Syntax
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Function call: “(fun arg1 arg2)”
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(+ 1 2 3)
Lists
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(list ‘3 ‘7 ‘apples)
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(3 7 apples)
(list ‘13 list(‘3 ‘5))
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(13 (3 5))
LISP – Innovations
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Garbage Collection
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If else statements
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Recursion
LISP – Linked Lists
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Car (first)
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Cdr (rest)
LISP - Examples

If then else
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(if nil
(list ‘2 ‘3)
(list ‘5 ‘6))
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One line variant:
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(if nil (list ‘2 ‘3) (list ‘5 ‘6))
LISP - Examples

Factorial
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(defun factorial (n)
(if (<= n 1)
1
(* n (factorial (- n 1)))))
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One line variant:
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(defun factorial (n) (if (<= n 1) 1 (* n (factorial (- n 1)))))
LISP - Examples
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Recursive List Size
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(defun recursiveSize (L)
(if (null L)
0
(1+ (recursiveSize(rest L)))))
LISP - Examples

Recursive List Sum with “LET”

(defun sum (L)
(if (null L)
0
(let
((S1 (first L))
(S2 (sum (rest L))))
+ S1 S2)))
LISP- Summary and Comparison

Readability

Writability
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Reliability
Python

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Developed early 1990’s
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Guido van Rossum
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ABC language
Python 2.0
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2000
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Community-supported -> reliability
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Modular; community expandable
Python 3.0
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2008
Python – Readability is Key
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Design goal
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One way to do things
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Clarity over clever code
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Whitespace over braces
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“pass” for No-Op
Python
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Writability
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Similar to other OO languages
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Verification support
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Interpreted, assert, no statements in conditions
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Clean style
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Few keywords
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Simple grammar -> few ways to do something
Python
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Comparisons
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== tests values, not references
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A < b <= C works properly
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Ternary operator readable
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“a if b else c”
Python
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System Requirements
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Cross platform
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Python Interpreter
Simplicity
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Small core language
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Large libaraies
Python - Examples

a = 15
if(a < 10):
print(“input less than 10”)
elif(10 < a < 20):
print(“input between 10 and 20”)
else:
print(“input greater than 20”)
Python - Examples

Function definition
def greatest(a, b, c):
largest = a if a > b else b
largest = largest if largest > c else c
print(largest)
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Function call
greatest(7, 3, 14)
14
Python - Examples

Determine if prime
def isPrime(num):
prime = True
for i in range(2, (num / 2) + 1):
if num % i == 0:
prime = False
return prime
def tenPrimes():
list = []
count = 0
current = 2
#store the first 10 primes in a list
while count < 10:
if isPrime(current):
count += 1
list.append(current)
current = current + 1
#print the list
for element in list:
print(element)
Python - Summary and Comparison

Readability
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Writability
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Reliability
Python - Examples
Demo