Getting Started with JSL¶

This guide provides a concise introduction to JSL to get you up and running in minutes. JSL is a lightweight, functional programming language that uses JSON for its syntax, making it ideal for data manipulation, configuration, and network-native applications.

Installation¶

JSL requires Python 3.8 or later.

From Source¶

Clone the repository and install JSL using pip:

git clone https://github.com/queelius/jsl.git
cd jsl
pip install -e .

Verify Installation¶

You can verify the installation by running a simple program or by starting the interactive REPL:

# Run a simple JSL program from the command line
echo '["print", "@Hello, JSL!"]' | jsl

# Start the interactive REPL
jsl --repl

Your First JSL Program¶

JSL programs are simply JSON data structures. Create a file named hello.jsl with the following content:

["print", "@Hello, World!"]

Execute it from your terminal:

jsl hello.jsl

You should see the output: Hello, World!

Note on File Extensions We recommend using the .jsl extension for your JSL program files. This helps distinguish them from regular JSON data files and allows for better editor integration. However, the jsl interpreter will happily run files with a .json extension, preserving the principle that all JSL code is valid JSON.

Core Concepts¶

Literals and Variables¶

Standard JSON literals like numbers, booleans, and null evaluate to themselves. Strings are used for both literal text and variable references. A string with an @ prefix is a literal, while a string without it is treated as a variable.

42          // A number
"@hello"    // A string literal
"my_variable" // A reference to a variable

Basic Operations¶

JSL uses prefix notation (like Lisp) for function calls. The first element of an array is the function to be called, and the rest are its arguments.

["+", 1, 2, 3]

This expression evaluates to 6.

Defining Variables and Functions¶

You can define variables with def and functions with lambda. The do special form lets you execute a sequence of expressions.

[
  "do",
  ["def", "x", 10],
  ["def", "square", ["lambda", ["n"], ["*", "n", "n"]]],
  ["square", "x"]
]

This evaluates to 100.

Conditional Logic¶

The if special form provides conditional evaluation:

["if", [">", 5, 3], "@Greater", "@Less"]

This evaluates to "Greater".

A Quick Example: Fibonacci¶

Here is a more complete example that defines a recursive function to compute Fibonacci numbers and then applies it to a list of numbers:

[
  "do",
  ["def", "fib",
   ["lambda", ["n"],
    ["if", ["<=", "n", 1],
     "n",
     ["+", ["fib", ["-", "n", 1]], ["fib", ["-", "n", 2]]]]]],
  ["map", "fib", ["list", 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]]
]

Running JSL Code¶

You can run JSL programs in several ways:

From a file: jsl your_program.jsl
From standard input: echo '["+", 1, 2]' | jsl
Using the REPL: jsl --repl
As a web service: jsl --service

Next Steps¶

Now that you have a basic understanding of JSL, you can explore the following sections for more in-depth information:

Language Guide: For a comprehensive overview of JSL's syntax and semantics.
Tutorials: For guided, step-by-step lessons.
Examples: For a collection of practical, real-world examples.