Category talk:ALGOL 68-rows

Source code

# rows.incl.a68: array related utilities for Algol 68 RC tasks                #

    # prints the elements of an array of integers separated by spaces         #
    OP   SHOW = ( []INT list )VOID:
         FOR i FROM LWB list TO UPB list DO
            print( ( " ", whole( list[ i ], 0 ) ) )
         OD # SHOW # ;
    # prints the elements of an array of reals separated by spaces            #
    OP   SHOW = ( []REAL list )VOID:
         FOR i FROM LWB list TO UPB list DO
            print( ( " ", fixed( list[ i ], -14, 8 ) ) )
         OD # SHOW # ;

    # operators and modes to allow "QUICKSORT x FROMELEMENT lb TOELEMENT ub"  #

    # mode to hold the lower and upper element indexes to sort                #
    MODE SORTBOUNDS = STRUCT( INT lb, ub );

    # unary operator that returns its argument                                #
    # if we were to support multiple sort methods, could retuen the array     #
    # plus a code to specify sorting using quicksort                          #
    OP QUICKSORT = ( REF[]INT  a )REF[]INT:  a;
    OP QUICKSORT = ( REF[]REAL a )REF[]REAL: a;

    # constructs a SORTBOUNDS from its parameters                             #
    PRIO TOELEMENT   = 9;
    OP   TOELEMENT   = ( INT lb, ub )SORTBOUNDS: SORTBOUNDS( lb, ub );

    # in-place quick sort an array                                            #
    PRIO FROMELEMENT = 8;
    # in-place quick sort an array of integers                                #
    OP   FROMELEMENT = ( REF[]INT a, SORTBOUNDS bounds )REF[]INT:
         IF INT lb = lb OF bounds;
            INT ub = ub OF bounds;
            ub <= lb
         THEN
            # empty array or only 1 element #
            a
         ELSE
            # more than one element, so must sort #
            INT left   := lb;
            INT right  := ub;
            # choosing the middle element of the array as the pivot #
            INT pivot  := a[ left + ( ( right + 1 ) - left ) OVER 2 ];
            WHILE
                WHILE IF left  <= ub THEN a[ left  ] < pivot ELSE FALSE FI
                DO
                    left  +:= 1
                OD;
                WHILE IF right >= lb THEN a[ right ] > pivot ELSE FALSE FI
                DO
                    right -:= 1
                OD;
                left <= right
            DO
                INT t      := a[ left  ];
                a[ left  ] := a[ right ];
                a[ right ] := t;
                left      +:= 1;
                right     -:= 1
            OD;
            QUICKSORT a FROMELEMENT lb   TOELEMENT right;
            QUICKSORT a FROMELEMENT left TOELEMENT ub;
            a
         FI # FROMELEMENT # ;
    # in-place quick sort an array of reals                                   #
    OP   FROMELEMENT = ( REF[]REAL a, SORTBOUNDS bounds )REF[]REAL:
         IF INT lb = lb OF bounds;
            INT ub = ub OF bounds;
            ub <= lb
         THEN
            # empty array or only 1 element #
            a
         ELSE
            # more than one element, so must sort #
            INT  left  := lb;
            INT  right := ub;
            # choosing the middle element of the array as the pivot #
            REAL pivot := a[ left + ( ( right + 1 ) - left ) OVER 2 ];
            WHILE
                WHILE IF left  <= ub THEN a[ left  ] < pivot ELSE FALSE FI
                DO
                    left  +:= 1
                OD;
                WHILE IF right >= lb THEN a[ right ] > pivot ELSE FALSE FI
                DO
                    right -:= 1
                OD;
                left <= right
            DO
                REAL t     := a[ left  ];
                a[ left  ] := a[ right ];
                a[ right ] := t;
                left      +:= 1;
                right     -:= 1
            OD;
            QUICKSORT a FROMELEMENT lb   TOELEMENT right;
            QUICKSORT a FROMELEMENT left TOELEMENT ub;
            a
         FI # FROMELEMENT # ;


# END rows.incl.a68                                                           #