add: Variables and Logic

[ThePat02]

This pull request introduces significant enhancements to the quill language and its interpreter, including support for variable declarations, assignments, conditional statements, and more robust expression handling. Additionally, it introduces a new example script showcasing these features. The changes span across the Abstract Syntax Tree (AST), interpreter logic, and the example script.

Language Features and Syntax Enhancements:

1. Expanded AST Support:

   • Added new expression types (BooleanLiteral, IntegerLiteral, InfixExpression, PrefixExpression, InterpolatedString) and statement types (LetStatement, AssignStatement, IfStatement) to support variable declarations, assignments, and conditional logic. ([[1]](https://github.com/ThePat02/quill/pull/1/files#diff-21a96fe9ac8432a6a8ab1a6270893e2f84419b176e4889bd8696b1720329b82aR50-R155), [[2]](https://github.com/ThePat02/quill/pull/1/files#diff-435c5aebaadc51c284cea54190e5ffa0de06a65190c20f0cf71db8f9077d672aL100-R249))
   • Enhanced existing AST node DialogStatement to support expressions for text, enabling interpolation and dynamic content. ([internal/ast/statements.goL31-R74](https://github.com/ThePat02/quill/pull/1/files#diff-435c5aebaadc51c284cea54190e5ffa0de06a65190c20f0cf71db8f9077d672aL31-R74))

2. Interpreter Updates:

   • Implemented execution logic for new statement types (LetStatement, AssignStatement, IfStatement) and expanded expression evaluation to handle interpolation, infix, and prefix operations. ([[1]](https://github.com/ThePat02/quill/pull/1/files#diff-584e5570407b02964ad571ea8ac4603bc6fdabbbcec9bb12734a3dac2909e748R97-L119), [[2]](https://github.com/ThePat02/quill/pull/1/files#diff-584e5570407b02964ad571ea8ac4603bc6fdabbbcec9bb12734a3dac2909e748R134-R232), [[3]](https://github.com/ThePat02/quill/pull/1/files#diff-584e5570407b02964ad571ea8ac4603bc6fdabbbcec9bb12734a3dac2909e748R530-R737))
   • Added variable storage and management (variables map) to track declared variables and their values during execution. ([[1]](https://github.com/ThePat02/quill/pull/1/files#diff-584e5570407b02964ad571ea8ac4603bc6fdabbbcec9bb12734a3dac2909e748R58), [[2]](https://github.com/ThePat02/quill/pull/1/files#diff-584e5570407b02964ad571ea8ac4603bc6fdabbbcec9bb12734a3dac2909e748R80))

Example Script:

1. New Example Script (examples/shop.q):
   • Introduced a shop simulation demonstrating variable handling, conditional logic, and dynamic text interpolation. The script includes features like purchasing items, checking wallet balance, and handling insufficient funds. ([examples/shop.qR1-R54](https://github.com/ThePat02/quill/pull/1/files#diff-599f96a6d1ef22cc0874f9fdd977700f047a90f04bcce49489db87acaa93d1c6R1-R54))

Code Robustness:

1. Improved String Representations:

   • Enhanced String() methods across AST nodes to handle nil cases gracefully, ensuring robust debugging and error handling. ([[1]](https://github.com/ThePat02/quill/pull/1/files#diff-21a96fe9ac8432a6a8ab1a6270893e2f84419b176e4889bd8696b1720329b82aR12-R14), [[2]](https://github.com/ThePat02/quill/pull/1/files#diff-21a96fe9ac8432a6a8ab1a6270893e2f84419b176e4889bd8696b1720329b82aR25-R27), [[3]](https://github.com/ThePat02/quill/pull/1/files#diff-21a96fe9ac8432a6a8ab1a6270893e2f84419b176e4889bd8696b1720329b82aR38-R40), [[4]](https://github.com/ThePat02/quill/pull/1/files#diff-644fc1ed5ebae9c40e2542a3450a224634d7e413997e9ebad135a02aad1c0fd6R22-R30), [[5]](https://github.com/ThePat02/quill/pull/1/files#diff-435c5aebaadc51c284cea54190e5ffa0de06a65190c20f0cf71db8f9077d672aL12-R19), [[6]](https://github.com/ThePat02/quill/pull/1/files#diff-435c5aebaadc51c284cea54190e5ffa0de06a65190c20f0cf71db8f9077d672aL22-R36), [[7]](https://github.com/ThePat02/quill/pull/1/files#diff-435c5aebaadc51c284cea54190e5ffa0de06a65190c20f0cf71db8f9077d672aL58-R117))

2. Error Handling:

   • Added detailed error reporting for undefined variables, invalid operations, and unsupported expression types in the interpreter. ([[1]](https://github.com/ThePat02/quill/pull/1/files#diff-584e5570407b02964ad571ea8ac4603bc6fdabbbcec9bb12734a3dac2909e748R134-R232), [[2]](https://github.com/ThePat02/quill/pull/1/files#diff-584e5570407b02964ad571ea8ac4603bc6fdabbbcec9bb12734a3dac2909e748R530-R737))

These changes collectively enhance the language's capabilities, making it more expressive and suitable for complex interactive narratives. The example script serves as a practical demonstration of these new features.

[Copilot]

Pull Request Overview

This PR enriches the Quill language with variable declarations, assignments, conditional logic, and enhanced interpolation, alongside a demonstration script.

• Expanded AST with LetStatement, AssignStatement, IfStatement, Boolean/Integer literals, infix/prefix expressions, and updated String() methods to guard against nil.
• Updated tokenizer and scanner to recognize new operators (+=, >=, &&, etc.) and keywords (LET, IF, ELSE, TRUE, FALSE).
• Enhanced interpreter to store variables, execute new statements, evaluate complex expressions, and report detailed errors; added examples/shop.q to showcase features.

Reviewed Changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/token/types.go	Added new operator tokens and variable keywords; updated comments
internal/scanner/scanner.go	Extended scanning logic for multi-character operators
internal/interpreter/interpreter.go	Introduced variable storage and execution for let/assign/if; expression evaluator updates
internal/ast/statements.go	Added AST nodes and String() guards for new statements
internal/ast/node.go	Added nil check in Program.String()
internal/ast/expressions.go	Added AST nodes and guards for new literals/expressions
examples/shop.q	New example script demonstrating variables and logic