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What are the characteristics of lisp language?
**Foreword**
In the eyes of some, Lisp is considered an "anti-intellectual" language that defies the logic of natural human language. It is often seen as having meaning only within mathematical logic and being limited to niche applications. However, despite its narrow scope, it is frequently recommended and promoted.
I believe that regarding different opinions about Lisp, we should be brave in practice and learn to judge for ourselves. Don’t dismiss or accept something without thinking and experimenting. These perspectives are simply meant to offer you a new angle and a starting point for exploration.
This article is just a personal summary of Lisp's characteristics and general observations. I apologize if there are any shortcomings.
**About Lisp Overview**
The programming language itself was not designed to conform to the logic of natural language. Its purpose is to help people develop software more efficiently, making it easier for machines to understand. Machine comprehension is the primary concern. Lisp is no different. Mathematical logic is just a set of rules, while Lisp is a practical realization, more adaptable and advanced than abstract theory.
Early programmers used Lisp extensively, but as software grew in scale, the need for more complex features became apparent. Lisp, known for its simplicity, struggled to keep up with evolving demands due to its minimalistic development environment. Yet, it can still develop existing software if one is willing to use it—there’s no reason it should ever fall behind other languages.
Many people admire Lisp, influenced by certain individuals who spark curiosity. But how many actually use it for real projects? I can't say for sure.
**View One: (Support)**
1. **Lisp is both advanced and fundamental**: Unlike Python or Ruby, which have built-in array and hash operations, Lisp data structures are typically made of two parts: `(AAA BBB)`. The first element, AAA, is called the *car*, and the rest, BBB, is the *cdr*. This basic structure, known as a cons cell, forms the foundation for complex data types like arrays, hash tables, and trees. So, is this not fundamental? Yet, Lisp is undeniably advanced. C is efficient at the machine level but lacks in developer productivity. According to *Hacker and Painter*, Lisp can achieve the same functionality with just 1/10th the code. Plus, it allows direct manipulation of CPU registers—something even advanced virtual machine languages struggle to match.
2. **Lisp is concise**: The syntax of Lisp can be summarized in one sentence: everything enclosed in parentheses is a list. The first item is treated as a function, and the rest as arguments. Elements preceded by a single quote are not evaluated and are returned as-is. That’s all. The truth, like `E = mc²`, is simple. Hence, Lisp is powerful.
Most languages, like C or Java, have reserved words, which separate statements from data and limit flexibility. Lisp has no reserved words. Instead, most atoms are symbols. For example, `(print atom-1 atom-2)` evaluates `atom-1` and `atom-2` as variables and passes them to the `print` function. If you write `(atom-1 print atom-2)`, it evaluates `print` and `atom-2`, then calls the function `atom-1`. This distinction between functions and variables is what gives Lisp its power.
Because data and code are the same in Lisp, it supports powerful macro systems. Macros take parameters and return code that is inserted directly into the program. Other languages can’t do this because they can’t distinguish between data and code. They return data, not executable code, which requires evaluation. Lisp, on the other hand, can replace parts of the source code dynamically, giving it unmatched flexibility.
But why hasn’t Lisp been widely adopted since 1958?
Lisp isn’t without application. It’s widely used in academic settings, such as MIT’s introductory courses using Scheme, and was even used by Paul Graham in his startup Viaweb, one of the first internet companies. However, its power comes with a trade-off: it's flexible but lacks strict grammar. Businesses prefer stability and ease of maintenance, which is why many opt for languages like Java or C++. As Matsumoto said, Lisp’s lack of grammar can be confusing, so Ruby added some structure to make it more user-friendly.
From a programmer’s perspective, most people aren’t as smart as hackers, and many prefer “dead†languages like Java or C++ because their thinking may be more rigid. Lisp is more suited for powerful hackers, not business environments.
In summary, Lisp is flexible and unconstrained. Once you use it, you might never want to go back. It has a harmonious beauty that reflects the truth of computing. While languages like Fortran, C++, and Java were born out of necessity, Lisp was created to pursue truth and beauty. Even after 50 years, it remains relevant.
**But from a realistic point of view, how can we use Lisp today?**
Emacs uses Emacs Lisp as its architectural language, which is a great way to learn. Common Lisp and Scheme are well-known dialects, though they are more commonly used in education than in commercial applications. The GNU project uses Guile, but it’s not widely known. Clojure, a Lisp dialect running on the JVM, is gaining popularity. It compiles to Java bytecode and integrates seamlessly with Java libraries, making it a powerful tool. It can also be compiled to JavaScript, opening up new possibilities. Node.js and other platforms support it too.
**View Two: (Not Supported)**
I believe Lisp will never become a mainstream programming language. Its failure to gain widespread adoption stems from its anti-human design. It prioritizes machine logic over human readability, much like binary code. Humans value diversity, and natural language has countless expressions. We choose decimal over binary because it offers more nuance. Lisp, with its S-expressions, suppresses this diversity by eliminating infix notation like A + B, which humans have used for centuries. This goes against human nature, leading to its rejection by most developers.
In short, Lisp violates the natural need for diversity in human expression and cannot become a mainstream language.
**Lisp Language Features**
Lisp is a functional programming language where all operations are implemented through functions acting on parameters.
It does not have traditional assignment statements or variables found in imperative languages. Repeated procedures can be expressed using recursive function calls instead of loops.
Lisp is an old functional language with weak typing and dynamic inference. Its code is composed of lists, and each entry can hold any type of data—numbers, functions, symbols, or sublists. During execution, these lists can be modified at any time.
The core operators in Lisp are only seven: `quote`, `atom`, `eq`, `car`, `cdr`, `cons`, and `cond`. The first three deal with symbol analysis; `car`, `cdr`, and `cons` manipulate lists; `cond` handles conditional branching. This minimal definition makes Lisp very close to the pure functional language of the Turing machine prototype, unmatched by modern languages.
However, Lisp's weak typing can lead to lower performance. The original design limits its scalability, requiring users to implement many features manually, resulting in numerous dialects.
**Lisp Advantages:**
- Unusual grammar acts as an IQ filter.
- Syntactic sugar is ideal for editor optimization, with no arbitrary restrictions.
- Emacs configuration is inherently personal. The codebase is small and easy to manage, avoiding quality issues in multi-person development.