Implement basic execution system and UI

This is a rather large commit that includes all of the following:
- React UI with code editor, runtime renderer and input-output panes
- Language providers for a sample language and Brainfuck
- Implementation of code execution in a web worker
- All-at-once unabortable execution of program fully functional

engines/types.ts

@@ -0,0 +1,71 @@
+import monaco from "monaco-editor";
+import React from "react";
+
+/**
+ * Type alias for defining range of characters to highlight in a single line.
+ * - Missing `start` means highlight starting from start of the line.
+ * - Missing `end` means highlight ending at the end of the line.
+ */
+export type CharRange = { start?: number; end?: number };
+
+/** Type denoting a range of text in document spanning within a line */
+export type DocumentRange = {
+  line: number;
+  charRange?: CharRange;
+};
+
+/** Source code token provider for the language, specific to Monaco */
+export type MonacoTokensProvider = monaco.languages.IMonarchLanguage;
+
+/** Type alias for props passed to renderer */
+export type RendererProps<RS> = { state: RS | null };
+
+/**
+ * Type alias for the result of engine executing a single step.
+ */
+export type StepExecutionResult<RS> = {
+  /** New props to be passed to the renderer */
+  rendererState: RS;
+
+  /** String to write to program output */
+  output?: string;
+
+  /**
+   * Used to highlight next line to be executed in the editor.
+   * Passing `null` indicates reaching the end of program.
+   */
+  nextStepLocation: DocumentRange | null;
+};
+
+/**
+ * Language engine is responsible for providing
+ * execution and debugging API to the platform.
+ */
+export interface LanguageEngine<RS> {
+  /** Load code and user input into the engine and prepare for execution */
+  prepare: (code: string, input: string) => void;
+
+  /** Perform a single step of code execution */
+  executeStep: () => StepExecutionResult<RS>;
+
+  /** Reset all state to prepare for new cycle */
+  resetState: () => void;
+}
+
+/**
+ * Language provider provides all language-specific
+ * functionality to the platform.
+ */
+export interface LanguageProvider<RS> {
+  /** Monaco-specific tokenizer for syntax highlighting */
+  editorTokensProvider?: MonacoTokensProvider;
+
+  /** Monaco-specific autocomplete provider */
+  autocompleteProvider?: any;
+
+  /** Sample code sample for the language */
+  sampleProgram: string;
+
+  /** React component for visualising runtime state */
+  Renderer: React.FC<RendererProps<RS>>;
+}