course n°4 · Découverte

Reading COBOL

1959 wrote the most readable code in the world — and it's your bridge from vibe coder to live coder.

~11 min7 stations
▶ video🧩 exercises📄 cheat sheet
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42 seconds · English captions included · 7.8 Mo

The 7 things you'll know how to do

Lesson 4: Reading COBOL

Regarde la leçon (42 s) : le code le plus lisible jamais écrit est aussi le tuteur le plus honnête que tu auras eu.

COBOL is a sentence

Traduis cette phrase COBOL en Ruby : « MOVE "salut" TO greeting » — le contenu part dans la variable `greeting`.

Conditions, in full words

Traduis : « IF MONTANT IS GREATER THAN 1000 » — avec `montant = 1500` ET `petit = 500`, la variable `gros` doit valoir true et `petit_gros` false.

The loop, in full words

Traduis : « PERFORM 3 TIMES / ADD 1 TO COMPTEUR » — `compteur` doit finir à 3 (il part de 0).

COMPUTE, no surprise

Traduis : « COMPUTE TOTAL = PRIX + TAXE » — avec `prix = 10` et `taxe = 2`, `total` doit valoir 12 (et suivre si prix change).

Read before you code

Ce paragraphe COBOL dit : `MOVE 5 TO x`, puis `ADD 2 TO x` (deux fois), puis `IF x IS GREATER THAN 8` → `MOVE "gros" TO verdict`. Écris le Ruby qui produit exactement ça.

Lesson 4: OK

Sans aide — traduis ce mini-paragraphe : `MOVE 0 TO total`, `ADD 3 TO total`, `ADD 4 TO total`, `IF total IS GREATER THAN 6 THEN MOVE "ok" TO verdict`. Résultat attendu : total = 7, verdict = "ok".

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📄 The cheat sheet

print it, stick it on your monitor, pretend it was your idea

📄 Cheat sheet — Reading COBOL (your vibe → live bridge)

COBOL isn't an old language. It's a mirror: code written in full words.

Why learn to READ COBOL

  1. It's text. No magic symbols — sentences. If you can read it, you're already reading logic.
  2. The grammar is universal. IF, PERFORM, COMPUTE = if, .times, =. The words change, the logic never.
  3. Banks still run on it. Understanding the past is understanding why the present looks like this.
  4. Vibe → live: a vibe coder copies, a live coder understands. This vocabulary is the bridge.

The COBOL → Ruby dictionary (4 lines and you're a translator)

COBOL (read it out loud) Ruby (write this)
MOVE "salut" TO greeting greeting = "salut"
IF MONTANT IS GREATER THAN 1000 if montant > 1000
PERFORM 3 TIMES + ADD 1 TO compteur 3.times { compteur += 1 }
COMPUTE TOTAL = PRIX + TAXE total = prix + taxe

The 3-step method

READ     → out loud, like a sentence from your mother
UNDERSTAND → who gives what to whom? (MOVE = gives, TO = to)
CODE     → the same thing, in Ruby

A whole paragraph, taken apart

MOVE 0 TO total.        total = 0
ADD 3 TO total.         total += 3
ADD 4 TO total.         total += 4
IF total IS GREATER THAN 6
   MOVE "ok" TO verdict.

→ total == 7 and verdict == "ok". You just read 1959 code. 😉 Without Google.

The 3 local quirks (for laughs, but true)

  • COBOL is written in CAPS everywhere — Ruby doesn't care, but read it anyway.
  • IS GREATER THAN = >, IS EQUAL TO = == (equality, not assignment — same confusion as C!).
  • No THEN in Ruby: if … is enough. COBOL wants one, Ruby doesn't.

Never say again

  • "the old folks' language" → the language that made code readable before everyone else
  • "I code blind" → you just translated a COBOL paragraph. Live coder suits you fine.

SlopCourse Microduck — from slop to clean code.