How to resolve the algorithm Inverted syntax step by step in the ALGOL 68 programming language

Published on 12 May 2024 09:40 PM
#Algol 68

How to resolve the algorithm Inverted syntax step by step in the ALGOL 68 programming language

Table of Contents

Problem Statement

Inverted syntax with conditional expressions In traditional syntax conditional expressions are usually shown before the action within a statement or code block: In inverted syntax, the action is listed before the conditional expression in the statement or code block: Inverted syntax with assignment In traditional syntax, assignments are usually expressed with the variable appearing before the expression: In inverted syntax, the expression appears before the variable: Task The task is to demonstrate support for inverted syntax forms within the language by showing both the traditional and inverted forms.

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Step by Step solution about How to resolve the algorithm Inverted syntax step by step in the ALGOL 68 programming language

Source code in the algol programming language

# Inverted assignment                                                                       #
# Assignment in Algol 68 is via ":=" which is automaically provided for all modes (types)   #
# However we could define e.g. "=:" as an inverted assignment operator but we would need to #
# define a separate operator for each mode, e.g. for integers and strings:                  #
PRIO =: = 1;
OP   =: = ( INT a,    REF INT    b )REF INT:    b := a;
OP   =: = ( STRING a, REF STRING b )REF STRING: b := a;
OP   =: = ( CHAR   a, REF STRING b )REF STRING: b := a;
INT a, b; STRING s;
    1 =: a;
a + 1 =: b;
  "?" =: s;
print( ( a, b, s, newline ) );

# There is one standard inverted assignment operator: +=: or PLUSTO which prepends a string #
# to another:                                                                               #
"bc"  =: s;
"b"  +=: s;
print( ( s, newline ) );

# Inverted Conditional Expressions                                                          #
# We could define an operator called WHEN perhaps, that would execute its left operand if   #
# the right operand was TRUE. However the left operand would need to be a PROC VOID so the  #
# syntax would not be as convientent as the standard IF-THEN-FI construct. E.g.:            #
PRIO WHEN = 1;
OP   WHEN = ( PROC VOID code, BOOL test )VOID: IF test THEN code FI;

( VOID: print( ( "NO",  newline ) ) ) WHEN a = b;  # the anonymous PROC VOID is not called  #
( VOID: print( ( "yes", newline ) ) ) WHEN a /= b  # the anonymous PROC VOID is called      #

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