Aether

Aether is an ethereal, tree-walk interpreted, custom programming language implemented entirely in Java 25. It features a custom recursive descent parser, block scoping with dynamically nested scopes, standard control-flow constructs, arrays, and arithmetic operations.

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Language Specifications & Grammar

Aether programs are composed of statements and declarations parsed using recursive descent according to the following formal BNF grammar:

• program $\rightarrow$ declaration* EOF
• declaration $\rightarrow$ varDecl | statement
• varDecl $\rightarrow$ "manifest" IDENTIFIER ( "=" expression )? ";"
• statement $\rightarrow$ block | exprStmt | ifStmt | whileStmt | printStmt
• block $\rightarrow$ "{" declaration* "}"
• exprStmt $\rightarrow$ expression ";"
• ifStmt $\rightarrow$ "flux" "(" expression ")" statement ( "else" statement )?
• whileStmt $\rightarrow$ "cycle" "(" expression ")" statement
• printStmt $\rightarrow$ "reveal" expression ";"
• expression $\rightarrow$ assignment
• assignment $\rightarrow$ IDENTIFIER "=" assignment | equality
• equality $\rightarrow$ comparison ( ( "!=" | "==" ) comparison )*
• comparison $\rightarrow$ term ( ( ">" | ">=" | "<" | "<=" ) term )*
• term $\rightarrow$ factor ( ( "-" | "+" ) factor )*
• factor $\rightarrow$ unary ( ( "/" | "*" ) unary )*
• unary $\rightarrow$ ( "!" | "-" ) unary | primary
• primary $\rightarrow$ NUMBER | STRING | "true" | "false" | "nil" | "(" expression ")" | IDENTIFIER | "[" arrayLiteral "]"
• arrayLiteral $\rightarrow$ expression ( "," expression )*

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Keywords & Syntax Syntax Cheat-Sheet

• manifest: Declares a variable.

  manifest greeting = "Hello, World!";
  manifest unchecked; // Defaults to nil
  

• reveal: Outputs evaluated expressions to standard output.

  reveal greeting;
  reveal 1 + 2 * 3;
  

• flux / else: Conditional branch execution.

  flux (x > 10) {
      reveal "greater than 10";
  } else {
      reveal "10 or less";
  }
  

• cycle: While-loop iteration control.

  manifest count = 0;
  cycle (count < 3) {
      count = count + 1;
      reveal count;
  }
  

• nil: Null/empty literal.
• Arrays: Array literals represent collection values.

  manifest scores = [90, 85, 95];
  reveal scores;
  

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Project Structure

• aether.lexer: Contains the Lexer, token representations, and enum definitions:
  • Token - Representation record of scanned tokens.
  • TokenType - Enum mapping standard Aether lexemes.
  • Lexer - Performs string tokenization.
• aether.ast: Holds the compiler AST definitions:
  • AST - Visitor interface and base expression/statement interfaces.
  • Concrete node classes (e.g. Binary, Literal, Block, Flux, Cycle).
• aether (root): Core parser, environment, interpreter, and application driver:
  • Environment - Resolves and manages lexical variable scopes.
  • Parser - Parses a Token list into an AST.
  • Interpreter - Executes the AST.
  • Aether - The application entrypoint supporting REPL and file execution.

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How to Build and Run

Prerequisites

• Java JDK 25
• Apache Maven

1. Package the Source Code

Package the Maven project:

mvn clean package

2. Run in Interactive REPL Mode

Type code dynamically line-by-line:

java -jar target/java-project-aether-1.0-SNAPSHOT.jar

Example Session:

aether> manifest text = "Hello Aether!";
aether> reveal text;
Hello Aether!
aether> reveal [1, 2, 3];
[1.0, 2.0, 3.0]

3. Run a Source File

Execute a script file (e.g., creating a script file test.aether) [script files must be inside the scripts folder inside the root directory of the project]:

java -jar java-project-aether-1.0-SNAPSHOT.jar hello.aether