Implement core Forth runtime: dictionary, codegen, outer interpreter, REPL

- Dictionary: linked-list word headers in simulated linear memory with
  create/find/reveal, case-insensitive lookup, IMMEDIATE flag support
- WASM codegen: IR-to-WASM translation via wasm-encoder with full
  validation; all stack, arithmetic, comparison, logic, memory, control
  flow, and return stack operations; wasmtime execution tests
- Outer interpreter: tokenizer, number parsing (decimal/$hex/#dec/%bin),
  interpret/compile dispatch, control structures (IF/ELSE/THEN,
  BEGIN/UNTIL, BEGIN/WHILE/REPEAT), RECURSE, comments, string output
- 40+ primitive words registered via JIT-compiled WASM modules linked
  to shared memory/globals/table
- Interactive REPL with rustyline, piped input, and file execution
- 145 tests passing across dictionary, codegen, and runtime

crates/cli/src/main.rs

@@ -1,6 +1,7 @@
 //! WAFER CLI: Interactive REPL and AOT compiler for WAFER Forth.
 
 use clap::Parser;
+use wafer_core::outer::ForthVM;
 
 /// WAFER: WebAssembly Forth Engine in Rust
 #[derive(Parser, Debug)]
@@ -21,21 +22,91 @@ struct Cli {
 fn main() -> anyhow::Result<()> {
     let cli = Cli::parse();
 
+    let mut vm = ForthVM::new()?;
+
     match cli.file {
-        Some(ref _file) => {
-            // TODO: Step 9 - Load and execute Forth file
-            eprintln!("WAFER: file execution not yet implemented");
+        Some(ref file) => {
+            let source = std::fs::read_to_string(file)?;
+            vm.evaluate(&source)?;
+            let output = vm.take_output();
+            if !output.is_empty() {
+                print!("{output}");
+            }
         }
         None => {
-            // TODO: Step 9 - Interactive REPL
-            println!(
-                "WAFER v{} - WebAssembly Forth Engine in Rust",
-                env!("CARGO_PKG_VERSION")
-            );
-            println!("Type BYE to exit.");
-            eprintln!("REPL not yet implemented");
+            // Check if stdin is a pipe (not a TTY)
+            if !atty_is_tty() {
+                // Non-interactive: read all of stdin and evaluate
+                let mut input = String::new();
+                std::io::Read::read_to_string(&mut std::io::stdin(), &mut input)?;
+                // Evaluate line-by-line to handle multi-line input
+                for line in input.lines() {
+                    match vm.evaluate(line) {
+                        Ok(()) => {
+                            let output = vm.take_output();
+                            if !output.is_empty() {
+                                print!("{output}");
+                            }
+                        }
+                        Err(e) => {
+                            eprintln!("Error: {e}");
+                        }
+                    }
+                }
+            } else {
+                // Interactive REPL
+                println!(
+                    "WAFER v{} - WebAssembly Forth Engine in Rust",
+                    env!("CARGO_PKG_VERSION")
+                );
+                println!("Type BYE to exit.");
+
+                let mut rl = rustyline::DefaultEditor::new()?;
+                loop {
+                    let prompt = if vm.is_compiling() { "  ] " } else { "> " };
+                    match rl.readline(prompt) {
+                        Ok(line) => {
+                            let trimmed = line.trim();
+                            if trimmed.eq_ignore_ascii_case("BYE") {
+                                break;
+                            }
+                            let _ = rl.add_history_entry(&line);
+                            match vm.evaluate(&line) {
+                                Ok(()) => {
+                                    let output = vm.take_output();
+                                    if !output.is_empty() {
+                                        print!("{output}");
+                                    }
+                                    if !vm.is_compiling() {
+                                        println!(" ok");
+                                    }
+                                }
+                                Err(e) => {
+                                    eprintln!("Error: {e}");
+                                }
+                            }
+                        }
+                        Err(
+                            rustyline::error::ReadlineError::Interrupted
+                            | rustyline::error::ReadlineError::Eof,
+                        ) => {
+                            break;
+                        }
+                        Err(e) => {
+                            eprintln!("Readline error: {e}");
+                            break;
+                        }
+                    }
+                }
+            }
         }
     }
 
     Ok(())
 }
+
+/// Check if stdin is a terminal (TTY).
+fn atty_is_tty() -> bool {
+    use std::io::IsTerminal;
+    std::io::stdin().is_terminal()
+}

crates/core/Cargo.toml

@@ -8,10 +8,10 @@ license.workspace = true
 [dependencies]
 wasm-encoder = { workspace = true }
 wasmparser = { workspace = true }
+wasmtime = { workspace = true }
 anyhow = { workspace = true }
 thiserror = { workspace = true }
 
 [dev-dependencies]
 proptest = { workspace = true }
 insta = { workspace = true }
-wasmtime = { workspace = true }

crates/core/src/dictionary.rs

@@ -297,9 +297,7 @@ impl Dictionary {
     /// Toggle the IMMEDIATE flag on the most recent word.
     pub fn toggle_immediate(&mut self) -> WaferResult<()> {
         if self.latest == 0 && self.here == DICTIONARY_BASE {
-            return Err(WaferError::CompileError(
-                "no word defined yet".to_string(),
-            ));
+            return Err(WaferError::CompileError("no word defined yet".to_string()));
         }
         let flags_addr = (self.latest + 4) as usize;
         if flags_addr >= self.memory.len() {