2 files changed, 302 insertions, 0 deletions
diff --git a/src/analysis/typecheck.c b/src/analysis/typecheck.c
new file mode 100644
index 0000000..4a172d8
--- /dev/null
+++ b/src/analysis/typecheck.c
@@ -0,0 +1,279 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "typecheck.h"
+
+// ** Internal Helpers **
+
+static void tc_error(TypeChecker *tc, Token t, const char *msg)
+{
+    fprintf(stderr, "Type Error at %s:%d:%d: %s\n", g_current_filename, t.line, t.col, msg);
+    tc->error_count++;
+}
+
+static void tc_enter_scope(TypeChecker *tc)
+{
+    Scope *s = malloc(sizeof(Scope));
+    s->symbols = NULL;
+    s->parent = tc->current_scope;
+    tc->current_scope = s;
+}
+
+static void tc_exit_scope(TypeChecker *tc)
+{
+    if (!tc->current_scope)
+    {
+        return;
+    }
+    Scope *old = tc->current_scope;
+    tc->current_scope = old->parent;
+
+    Symbol *sym = old->symbols;
+    while (sym)
+    {
+        Symbol *next = sym->next;
+        free(sym);
+        sym = next;
+    }
+    free(old);
+}
+
+static void tc_add_symbol(TypeChecker *tc, const char *name, Type *type, Token t)
+{
+    Symbol *s = malloc(sizeof(Symbol));
+    memset(s, 0, sizeof(Symbol));
+    s->name = strdup(name);
+    s->type_info = type;
+    s->decl_token = t;
+    s->next = tc->current_scope->symbols;
+    tc->current_scope->symbols = s;
+}
+
+static Symbol *tc_lookup(TypeChecker *tc, const char *name)
+{
+    Scope *s = tc->current_scope;
+    while (s)
+    {
+        Symbol *curr = s->symbols;
+        while (curr)
+        {
+            if (0 == strcmp(curr->name, name))
+            {
+                return curr;
+            }
+            curr = curr->next;
+        }
+        s = s->parent;
+    }
+    return NULL;
+}
+
+// ** Node Checkers **
+
+static void check_node(TypeChecker *tc, ASTNode *node);
+
+static void check_block(TypeChecker *tc, ASTNode *block)
+{
+    tc_enter_scope(tc);
+    ASTNode *stmt = block->block.statements;
+    while (stmt)
+    {
+        check_node(tc, stmt);
+        stmt = stmt->next;
+    }
+    tc_exit_scope(tc);
+}
+
+static int check_type_compatibility(TypeChecker *tc, Type *target, Type *value, Token t)
+{
+    if (!target || !value)
+    {
+        return 1; // Can't check
+    }
+
+    // Simple equality check for now... This will be changed.
+    if (!type_eq(target, value))
+    {
+
+        // For now we have strict equality on structure.
+
+        // In Zen C (like C), void* is generic.
+        if (TYPE_POINTER == target->kind && TYPE_VOID == target->inner->kind)
+        {
+            return 1;
+        }
+        if (TYPE_POINTER == value->kind && TYPE_VOID == value->inner->kind)
+        {
+            return 1;
+        }
+
+        // Exception: integer promotion/demotion.
+
+        if (target->kind >= TYPE_I8 && target->kind <= TYPE_U64 && value->kind >= TYPE_I8 &&
+            value->kind <= TYPE_U64)
+        {
+            return 1;
+        }
+
+        char *t_str = type_to_string(target);
+        char *v_str = type_to_string(value);
+        char msg[256];
+        snprintf(msg, 255, "Type mismatch: expected '%s', got '%s'", t_str, v_str);
+        tc_error(tc, t, msg);
+        free(t_str);
+        free(v_str);
+        return 0;
+    }
+    return 1;
+}
+
+static void check_var_decl(TypeChecker *tc, ASTNode *node)
+{
+    if (node->var_decl.init_expr)
+    {
+        check_node(tc, node->var_decl.init_expr);
+
+        Type *decl_type = node->type_info;
+        Type *init_type = node->var_decl.init_expr->type_info;
+
+        if (decl_type && init_type)
+        {
+            check_type_compatibility(tc, decl_type, init_type, node->token);
+        }
+    }
+
+    // If type is not explicit, we should ideally infer it from init_expr.
+    Type *t = node->type_info;
+    if (!t && node->var_decl.init_expr)
+    {
+        t = node->var_decl.init_expr->type_info;
+    }
+
+    tc_add_symbol(tc, node->var_decl.name, t, node->token);
+}
+
+static void check_function(TypeChecker *tc, ASTNode *node)
+{
+    // Just to suppress the warning.
+    (void)tc_error;
+
+    tc->current_func = node;
+    tc_enter_scope(tc);
+
+    for (int i = 0; i < node->func.arg_count; i++)
+    {
+        if (node->func.param_names && node->func.param_names[i])
+        {
+            tc_add_symbol(tc, node->func.param_names[i], NULL, (Token){0});
+        }
+    }
+
+    check_node(tc, node->func.body);
+
+    tc_exit_scope(tc);
+    tc->current_func = NULL;
+}
+
+static void check_expr_var(TypeChecker *tc, ASTNode *node)
+{
+    Symbol *sym = tc_lookup(tc, node->var_ref.name);
+    if (!sym)
+    {
+        // Check global functions/contexts if not found in locals
+        // This is a naive check.
+        // We really want to warn here if it's truly unknown.
+    }
+    if (sym && sym->type_info)
+    {
+        node->type_info = sym->type_info;
+    }
+}
+
+static void check_node(TypeChecker *tc, ASTNode *node)
+{
+    if (!node)
+    {
+        return;
+    }
+
+    switch (node->type)
+    {
+    case NODE_ROOT:
+        check_node(tc, node->root.children);
+        break;
+    case NODE_BLOCK:
+        check_block(tc, node);
+        break;
+    case NODE_VAR_DECL:
+        check_var_decl(tc, node);
+        break;
+    case NODE_FUNCTION:
+        check_function(tc, node);
+        break;
+    case NODE_EXPR_VAR:
+        check_expr_var(tc, node);
+        break;
+    case NODE_RETURN:
+        if (node->ret.value)
+        {
+            check_node(tc, node->ret.value);
+        }
+
+        break;
+
+    // Control flow with nested nodes.
+    case NODE_IF:
+        check_node(tc, node->if_stmt.condition);
+        check_node(tc, node->if_stmt.then_body);
+        check_node(tc, node->if_stmt.else_body);
+        break;
+    case NODE_WHILE:
+        check_node(tc, node->while_stmt.condition);
+        check_node(tc, node->while_stmt.body);
+        break;
+    case NODE_FOR:
+        tc_enter_scope(tc); // For loop init variable is scoped
+        check_node(tc, node->for_stmt.init);
+        check_node(tc, node->for_stmt.condition);
+        check_node(tc, node->for_stmt.step);
+        check_node(tc, node->for_stmt.body);
+        tc_exit_scope(tc);
+        break;
+    case NODE_EXPR_BINARY:
+        check_node(tc, node->binary.left);
+        check_node(tc, node->binary.right);
+        break;
+    case NODE_EXPR_CALL:
+        check_node(tc, node->call.callee);
+        check_node(tc, node->call.args);
+        break;
+    default:
+        // Generic recursion for lists.
+        break;
+    }
+
+    if (node->next)
+    {
+        check_node(tc, node->next);
+    }
+}
+
+// ** Entry Point **
+
+int check_program(ParserContext *ctx, ASTNode *root)
+{
+    TypeChecker tc = {0};
+    tc.pctx = ctx;
+
+    printf("[TypeCheck] Starting semantic analysis...\n");
+    check_node(&tc, root);
+
+    if (tc.error_count > 0)
+    {
+        printf("[TypeCheck] Found %d errors.\n", tc.error_count);
+        return 1;
+    }
+    printf("[TypeCheck] Passed.\n");
+    return 0;
+}
diff --git a/src/analysis/typecheck.h b/src/analysis/typecheck.h
new file mode 100644
index 0000000..fe51c4d
--- /dev/null
+++ b/src/analysis/typecheck.h
@@ -0,0 +1,23 @@
+#ifndef TYPECHECK_H
+#define TYPECHECK_H
+
+#include "ast.h"
+#include "parser.h"
+
+// Type Checker Context
+// Holds the state during the semantic analysis pass.
+// Unlike the parser, this focuses on semantic validity (types, definitions).
+typedef struct TypeChecker
+{
+    ParserContext *pctx;   // Reference to global parser context (for lookups)
+    Scope *current_scope;  // Current lexical scope
+    ASTNode *current_func; // Current function being checked (for return type checks)
+    int error_count;       // Number of errors found
+    int warning_count;     // Number of recommendations/warnings
+} TypeChecker;
+
+// Main Entry Point
+// Returns 0 on success (no errors), non-zero if errors occurred.
+int check_program(ParserContext *ctx, ASTNode *root);
+
+#endif // TYPECHECK_H