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Mark Di Marco

@markmarkoh.bsky.social

Early stage startup engineer and engineering leader, currently VP of Eng at Buildforce. Recording episodes of a new show called Commit History, which explores interesting commit on interesting open source projects markmarkoh.com

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Mark Di Marco @markmarkoh.bsky.social · 12/04/2025

Is this vibe coding? Asking for a friend.

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Mark Di Marco @markmarkoh.bsky.social · 01/12/2024

The Day 1 #AdventOfCode solution we've all been waiting for: COBOL 65 years ago a committee met in the Pentagon to standardize a new programming language, and soon COBOL-60 was born. Can you guess the name of the sorting algorithm used in the SORT-ARRAYS procedure? adventofcode.com/2024/day/1

Screenshot of code Preamble in COBOL:
IDENTIFICATION DIVISION.
PROGRAM-ID. NUMBER-PAIRING.

ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT INPUT-FILE ASSIGN TO "INPUT.TXT"
ORGANIZATION IS LINE SEQUENTIAL.

DATA DIVISION.
FILE SECTION.
FD INPUT-FILE.
01 INPUT-LINE.
05 LEFT-NUM PIC X(5).
05 FILLER PIC X(3).
05 RIGHT-NUM PIC X(5).

WORKING-STORAGE SECTION.
01 WS-ARRAYS.
05 LEFT-ARRAY OCCURS 1000 TIMES PIC S9(5).
05 RIGHT-ARRAY OCCURS 1000 TIMES PIC S9(5).

01 WS-VARIABLES.
05 EOF-FLAG PIC X VALUE 'N'.
05 ARRAY-SIZE PIC 9(4) VALUE 0.
05 TOTAL-DIST PIC 9(8) VALUE 0.
05 TEMP-NUM PIC S9(5).
05 I PIC 9(4).
05 J PIC 9(4).
05 DIFF PIC S9(5).

PROCEDURE DIVISION.
MAIN-PROCEDURE.
DISPLAY "=== STARTING PROGRAM ==="
OPEN INPUT INPUT-FILE
PERFORM READ-NUMBERS UNTIL EOF-FLAG = 'Y'
CLOSE INPUT-FILE

DISPLAY "=== SORTING ARRAYS ==="
PERFORM SORT-ARRAYS

DISPLAY "=== CALCULATING DISTANCES ==="
PERFORM CALCULATE-DISTANCE

DISPLAY "=== FINAL RESULT ==="
DISPLAY "TOTAL DISTANCE: " TOTAL-DIST
STOP RUN.

Screenshot of main procedures in COBOL for day 1 of advent of code solution:
READ-NUMBERS.
READ INPUT-FILE
AT END MOVE 'Y' TO EOF-FLAG
NOT AT END
ADD 1 TO ARRAY-SIZE
MOVE FUNCTION NUMVAL(LEFT-NUM) TO LEFT-ARRAY(ARRAY-SIZE)
MOVE FUNCTION NUMVAL(RIGHT-NUM) TO RIGHT-ARRAY(ARRAY-SIZE)
END-READ.

SORT-ARRAYS.
PERFORM VARYING I FROM 1 BY 1
UNTIL I > ARRAY-SIZE - 1
PERFORM VARYING J FROM 1 BY 1
UNTIL J > ARRAY-SIZE - I
IF LEFT-ARRAY(J) > LEFT-ARRAY(J + 1)
MOVE LEFT-ARRAY(J) TO TEMP-NUM
MOVE LEFT-ARRAY(J + 1) TO LEFT-ARRAY(J)
MOVE TEMP-NUM TO LEFT-ARRAY(J + 1)
END-IF
IF RIGHT-ARRAY(J) > RIGHT-ARRAY(J + 1)
MOVE RIGHT-ARRAY(J) TO TEMP-NUM
MOVE RIGHT-ARRAY(J + 1) TO RIGHT-ARRAY(J)
MOVE TEMP-NUM TO RIGHT-ARRAY(J + 1)
END-IF
END-PERFORM
END-PERFORM.

CALCULATE-DISTANCE.
PERFORM VARYING I FROM 1 BY 1
UNTIL I > ARRAY-SIZE
COMPUTE DIFF = LEFT-ARRAY(I) - RIGHT-ARRAY(I)
IF DIFF < 0
COMPUTE DIFF = DIFF * -1
END-IF
ADD DIFF TO TOTAL-DIST
END-PERFORM.

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Mark Di Marco @markmarkoh.bsky.social · 01/12/2024

I look for commits in all sorts of programming languages, and so far throughout my research, Zig has been my favorite “new” language that not enough people are talking about. Here were a few patterns from my Bun.sh episode that stuck out: @ziglang.bsky.social

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