About Python Syntax

[Hung, Le Khanh]

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Best regards
============
Dear Sirs and Mmes.

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Thank you.

 

We are interested in Programming Language Methodology in general and in Language Structure for long time.

When i first have seen Python, i was deeply impresed by its simplicity and usability, especialy for beginers.

Before, we have developed some control structures for Programming Language and now would like to deliver here. 

The Python's unstructured statements like break, continue, while, if elseif else could be replaced by more declarative

 

The short sketch of these structures:

(some of keywords has been used for other's Python statement so we had to use some other symbol. But it play no important role for describing our main concept. I tryed to use Python's Syntax description)

 

CompoudStatement ::= dostatement | loop statement

dostatement::=

 

"do" suite

GuardedCommand

 

loopstatement::=

"loop" suite

GuardedCommand

 

GuardedCommand::=

    ( ?[!] "check" Condition  suite )*

 

Condition ::= expression :

Condition ::=

( "case" Condition suite )*

 

In my opinion those constructions could replace all Python's compound statements

 

Some examples:

 

if B1 : S1

elif B2 : S2

else S3

 

is equivalent to

 

do

?! check  case B1 : S1

              case B2 : S2

        S3

 

while B : S

 

is equivalent to

 

loop 

? check B : S

 


Here is the more practical example:

# Search in Array

# This is common sketch for searching algorithms

InitSearchScope

loop

? check NotEmptySearchScope: 

        TakeAnElement

? check NotFit: 

        SrinkSearchScope

# Implementation of Sequential Search

i = lo;  # Scope is from lo to hi

loop

? check i < hi : # i is in Scope

? check a[i] != x : 

        i+=1 

# Binary Search

i,j = lo,hi

loop

? check i<j : k = (i+j) / 2

? check 

        case a[k]<x : i = k+1

        case a[k]>x : j = k-1

 

This bit of code has the same structure as the previous!



# For comparison, here is Python's Binary search

i,j = lo,hi

while i<j : k = (i+j) / 2

        if a[k]<x : i = k+1

        elseif a[k]>x : j = k-1

        else break



The more important reason for introduction of new control structures for Python is the possibility of making a fullly visual interactive IDE for Python. Programmer would be not able to make syntax errors!

 

Best regards.

Hung 

 

 

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