fix: correct Cell union and add interpreter, main, word implementations

Co-authored-by: aider (openrouter/tencent/hy3-preview:free) <aider@aider.chat>

forth_interp.c

@@ -0,0 +1,97 @@
+#include "forth.h"
+
+// Input tokenizer
+char* next_token(void) {
+    if (input_ptr == NULL) return NULL;
+    while (*input_ptr != '\0' && isspace((unsigned char)*input_ptr)) {
+        input_ptr++;
+    }
+    if (*input_ptr == '\0') return NULL;
+    char* start = input_ptr;
+    while (*input_ptr != '\0' && !isspace((unsigned char)*input_ptr)) {
+        input_ptr++;
+    }
+    if (*input_ptr != '\0') {
+        *input_ptr = '\0';
+        input_ptr++;
+    }
+    return start;
+}
+
+// Interpreter functions
+void inner_interpreter(void) {
+    while (ip != NULL) {
+        Cell current = *ip;
+        ip++; // Move to next cell
+        current.word->code(current.word);
+    }
+}
+
+void process_token(const char* token) {
+    Word* w = lookup_word(token);
+    if (w != NULL) {
+        if (state == 0) { // Interpret mode
+            if (w->code == do_docolon) { // Colon definition
+                ret_push(NULL); // Return address to stop interpreter
+                ip = w->body;
+                inner_interpreter();
+            } else { // Primitive word
+                w->code(w);
+            }
+        } else { // Compile mode
+            if (w->flags & (1 << 7)) { // Immediate word: execute now
+                if (w->code == do_docolon) {
+                    ret_push(NULL);
+                    ip = w->body;
+                    inner_interpreter();
+                } else {
+                    w->code(w);
+                }
+            } else { // Normal word: compile into current definition
+                if (compile_idx >= COMPILE_BUF_SIZE) {
+                    printf("Compile buffer full\n");
+                    return;
+                }
+                compile_buf[compile_idx++] = (Cell){.word = w};
+            }
+        }
+    } else { // Not a known word: try to parse as number
+        char* end;
+        long v = strtol(token, &end, 10);
+        if (end != token && *end == '\0') { // Valid integer
+            if (state == 0) { // Interpret mode: push number
+                data_push((int32_t)v);
+            } else { // Compile mode: compile lit + number
+                Word* lit_w = lookup_word("lit");
+                if (lit_w == NULL) {
+                    printf("Fatal: lit word not found\n");
+                    return;
+                }
+                if (compile_idx + 2 > COMPILE_BUF_SIZE) {
+                    printf("Compile buffer full\n");
+                    return;
+                }
+                compile_buf[compile_idx++] = (Cell){.word = lit_w};
+                compile_buf[compile_idx++] = (Cell){.num = (int32_t)v};
+            }
+        } else {
+            printf("Unknown word: '%s'\n", token);
+        }
+    }
+}
+
+void outer_interpreter(void) {
+    while (1) {
+        printf("ok ");
+        fflush(stdout);
+        if (fgets(input_buf, INPUT_BUF_SIZE, stdin) == NULL) {
+            break; // EOF
+        }
+        input_ptr = input_buf;
+        char* tok;
+        while ((tok = next_token()) != NULL) {
+            process_token(tok);
+        }
+    }
+    printf("\n");
+}