Phase 2: variables, arrays, program execution, and control flow

Add variable storage (scalar and array), program line storage with
RUN/LIST/NEW, and full control flow: FOR/NEXT, GOTO, GOSUB/RETURN,
IF/THEN/ELSE, WHILE/WEND, ON GOTO/GOSUB, DATA/READ/RESTORE.

New modules: interp.c (1445 lines - execution loop and statement
dispatcher), vars.c, arrays.c, input.c. Version bumped to 0.2.0.
16 test programs pass including Leibniz pi and prime sieve.

include/gwbasic.h

@@ -10,7 +10,7 @@
 #include "gw_math.h"
 #include "strings.h"
 
-#define GW_VERSION "0.1.0"
+#define GW_VERSION "0.2.0"
 #define GW_BANNER "GW-BASIC " GW_VERSION
 
 /* Tokenizer */
@@ -22,4 +22,29 @@ void gw_stmt_print(void);
 void gw_print_value(gw_value_t *v);
 void gw_print_newline(void);
 
+/* Variables (vars.c) */
+gw_valtype_t gw_parse_varname(char name_out[2]);
+var_entry_t *gw_var_find_or_create(const char name[2], gw_valtype_t type);
+void gw_var_assign(var_entry_t *var, gw_value_t *val);
+void gw_vars_clear(void);
+void gw_stmt_deftype(gw_valtype_t type);
+void gw_stmt_swap(void);
+
+/* Arrays (arrays.c) */
+void gw_stmt_dim(void);
+gw_value_t *gw_array_element(const char name[2], gw_valtype_t type);
+void gw_stmt_erase(void);
+void gw_stmt_option(void);
+void gw_arrays_clear(void);
+
+/* Input (input.c) */
+void gw_stmt_input(void);
+void gw_stmt_line_input(void);
+
+/* DEF FN evaluation (interp.c) */
+gw_value_t gw_eval_fn_call(void);
+
+/* Error recovery for run loop */
+extern jmp_buf gw_run_jmp;
+
 #endif

include/interp.h

@@ -24,9 +24,43 @@ typedef struct {
     /* Default variable types for A-Z (DEFTBL) */
     gw_valtype_t def_type[26];
 
+    /* Variable storage */
+    var_entry_t vars[256];
+    int var_count;
+    array_entry_t arrays[64];
+    int array_count;
+    int option_base;
+
+    /* Control flow stacks */
+    for_entry_t for_stack[16];
+    int for_sp;
+    gosub_entry_t gosub_stack[24];
+    int gosub_sp;
+    while_entry_t while_stack[16];
+    int while_sp;
+
+    /* DEF FN */
+    fn_def_t fn_defs[26];
+
+    /* Run state */
+    program_line_t *cur_line;
+    bool running;
+
+    /* CONT state */
+    uint8_t *cont_text;
+    program_line_t *cont_line;
+
     /* DATA pointer */
     uint8_t *data_ptr;
+    program_line_t *data_line_ptr;
     uint16_t data_line;
+
+    /* Error trapping */
+    uint16_t on_error_line;
+    bool in_error_handler;
+    uint8_t *err_resume_text;
+    program_line_t *err_resume_line;
+    uint16_t err_line_num;
 } interp_state_t;
 
 extern interp_state_t gw;
@@ -35,8 +69,15 @@ extern interp_state_t gw;
 #define LINE_DIRECT 65535
 
 void gw_init(void);
-void gw_exec_line(uint8_t *tokens);
 void gw_exec_direct(const char *line);
+void gw_exec_stmt(void);
+void gw_run_loop(void);
+
+/* Program storage */
+void gw_store_line(uint16_t num, uint8_t *tokens, int len);
+void gw_delete_line(uint16_t num);
+program_line_t *gw_find_line(uint16_t num);
+void gw_free_program(void);
 
 /* CHRGET/CHRGOT - advance/peek the text pointer */
 uint8_t gw_chrget(void);

include/types.h

@@ -44,6 +44,48 @@ typedef struct {
     gw_value_t val;
 } var_entry_t;
 
+/* Array entry */
+typedef struct {
+    char name[2];
+    gw_valtype_t type;
+    int ndims;
+    int dims[8];        /* max dimensions per DIM */
+    int total_elements;
+    gw_value_t *data;   /* malloc'd flat array */
+} array_entry_t;
+
+/* FOR stack entry */
+typedef struct {
+    var_entry_t *var;
+    gw_value_t limit, step;
+    uint8_t *loop_text;
+    struct program_line *loop_line;
+    uint16_t line_num;
+} for_entry_t;
+
+/* GOSUB stack entry */
+typedef struct {
+    uint8_t *ret_text;
+    struct program_line *ret_line;
+    uint16_t line_num;
+} gosub_entry_t;
+
+/* WHILE stack entry */
+typedef struct {
+    uint8_t *while_text;
+    struct program_line *while_line;
+    uint16_t line_num;
+} while_entry_t;
+
+/* DEF FN entry */
+typedef struct {
+    bool defined;
+    char param_name[2];
+    gw_valtype_t param_type, ret_type;
+    uint8_t *body_text;
+    struct program_line *body_line;
+} fn_def_t;
+
 /* MBF (Microsoft Binary Format) types for file compatibility */
 typedef struct {
     uint8_t mantissa[3];