# 🧭 The Way of Programming

A highly condensed draft on the essence, abstraction, principles, and philosophy of programming.
It is not a tutorial, but "The Way": the structure of thought.

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# 1. Ontology of Programs: What is a Program?

-   Program = Data + Functions
-   Data is facts; functions are intentions
-   Input → Process → Output
-   State determines the form of the world, transformation depicts the process
-   A program is a description of reality, and also a tool to change reality.

**In one sentence: A program is structured thought.**

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# 2. Three Core Elements: Data · Functions · Abstraction

## Data
- Data is "existence"
- Data structure is the structure of thought
- If data is clear, the program is natural

<h2>Functions</h2>
- Functions are "change"
- Process is causality
- Logic should be transformation, not manipulation

<h2>Abstraction</h2>
- Abstraction is to filter out the false and preserve the true.
- Abstraction is not simplification, but extraction of essence.
- Hide what is unnecessary, expose what is necessary.

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# 3. Paradigm Evolution: From Doing to Purpose

<h2>Procedural Programming</h2>
- The world is composed of "steps"
- Process-driven
- Control flow is king

<h2>Object-Oriented Programming</h2>
- The world is composed of "things"
- State + Behavior
- Encapsulate complexity

<h2>Purpose-Oriented Programming</h2>
- The world is composed of "intentions"
- Talk about requirements, not steps.
- From imperative → declarative → intentional.

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# 4. Design Principles: Rules for Maintaining Order

<h2>High Cohesion</h2>
- Related things are close
- Unrelated things are isolated
- Single responsibility is the core of cohesion

<h2>Low Coupling</h2>
- Modules are like planets: predictable, but not bound.
- The fewer dependencies, the longer the life.
- Freedom comes from not being coupled.

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# 5. System View: Treating Programs as Systems

<h2>State</h2>
- The root of all errors is improper state.
- The less state, the more stable the program.
- Externalize state, limit state, automatically manage state.

<h2>Transformation</h2>
- Programs are not operations, but continuous changes.
- Every system can be viewed as:
  `output = transform(input)`

<h2>Composability</h2>
- Small units → Composable
- Composable → Reusable
- Reusable → Evolvable

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# 6. Way of Thinking: The Programmer's Mind

<h2>Declarative vs. Imperative</h2>
- Imperative: tell the system how to do it.
- Declarative: tell the system what you want.
- High-level code should be declarative.
- Low-level code can be imperative.

<h2>Specification Precedes Implementation</h2>
- Behavior precedes structure.
- Structure precedes code.
- A program is the shadow of its specification.

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# 7. Stability and Evolution: Making Programs Live Longer

<h2>Stable Interfaces, Unstable Implementations</h2>
- API is a contract.
- Implementation is detail.
- Not breaking the contract is being responsible.

<h2>Conservation of Complexity</h2>
- Complexity does not disappear, it only shifts.
- Either you bear it, or the user bears it.
- Good design converges complexity internally.

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# 8. Laws of Complex Systems: How to Manage Complexity

<h2>Local Simplicity, Global Complexity</h2>
- Every module should be simple.
- Complexity comes from composition, not modules.

<h2>Hidden Dependencies Are Most Dangerous</h2>
- Explicit > Implicit
- Transparent > Elegant
- Implicit dependencies are the beginning of decay.

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# 9. Reasonability

- Predictability is more important than performance.
- Programs should be reason-able by the human mind.
- Few variables, shallow branches, clear states, flat logic.
- Reasonability = Maintainability.

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# 10. Time Perspective

- A program is not a spatial structure, but a temporal structure.
- Every piece of logic is an event unfolding over time.
- Design must answer three questions:
  1. Who holds the state?
  2. When does the state change?
  3. Who triggers the change?

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# 11. Interface Philosophy

<h2>API is Language</h2>
- Language shapes thought.
- Good interfaces prevent misuse.
- Perfect interfaces make misuse impossible.

<h2>Backward Compatibility is Responsibility</h2>
- Breaking an interface = Breaking trust.

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# 12. Errors and Invariants

<h2>Errors are Normal</h2>
- Defaults are errors.
- Correctness requires proof.

<h2>Invariants Keep the World Stable</h2>
- Invariants are the physical laws of programs.
- Explicit constraints = Creating order.

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# 13. Evolvability

- Software is not a statue, but an ecosystem.
- Good design is not optimal, but changeable.
- The best code is the code your future self can understand.

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# 14. Tools and Efficiency

<h2>Tools Amplify Habits</h2>
- Good habits are amplified into efficiency.
- Bad habits are amplified into disaster.

<h2>Use tools, don't be used by them</h2>
- Understanding "why" is more important than "how".

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# 15. Mental Models

- Models determine understanding.
- Understanding determines code.
- Correct models are more important than correct code.

Typical models:
- Program = Data flow
- UI = State machine
- Backend = Event-driven system
- Business logic = Invariant system

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# 16. Principle of Least Surprise

- Good code should behave like common sense.
- No surprise is the best user experience.
- Predictability = Trust.

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# 17. High-Frequency Abstraction: Higher-Order Programming Philosophy

<h2>Program as Knowledge</h2>
- Code is the precise expression of knowledge.
- Programming is formalizing vague knowledge.

<h2>Program as Simulation</h2>
- All software is a simulation of reality.
- The closer the simulation is to essence, the simpler the system.

<h2>Program as Language</h2>
- The essence of programming is language design.
- All programming is DSL design.

<h2>Program as Constraint</h2>
- Constraints shape structure.
- Constraints are more important than freedom.

<h2>Program as Decision</h2>
- Every line of code is a decision.
- Delaying decisions = Preserving flexibility.

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# 18. Quotes

- Data is facts, functions are intentions.
- Program is causality.
- Abstraction compresses the world.
- The less state, the clearer the world.
- Interface is contract, implementation is detail.
- Composition over inheritance.
- Program is a temporal structure.
- Invariants stabilize logic.
- Reasonability over performance.
- Constraints create order.
- Code is the shape of knowledge.
- Stable interface, fluid implementation.
- No surprise is the highest design.
- Simplicity is the ultimate sophistication.

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# Conclusion

**The Way of Programming does not teach you how to write code, but how to understand the world.**
Code is the shape of thought.
A program is another language for understanding the world.

May you remain clear in a complex world, and see the essence in code.
