3 files changed, 41 insertions, 43 deletions

diff --git a/ast.c b/ast.c
index 4663cd2..760f259 100644
--- a/ast.c
+++ b/ast.c
@@ -130,15 +130,7 @@ void free_ast(ASTNode *node) {
   free(node);
 }
 
-typedef struct Env {
-  char *name;
-  int val;
-  struct Env *next;
-} Env;
-
-static Env *env = NULL;
-
-static int env_lookup(const char *name) {
+static int env_lookup(Env *env, const char *name) {
   for (Env *e = env; e; e = e->next) {
     if (strcmp(e->name, name) == 0)
       return e->val;
@@ -147,8 +139,8 @@ static int env_lookup(const char *name) {
   exit(EXIT_FAILURE);
 }
 
-static void env_update(const char *name, int val) {
-  for (Env *e = env; e; e = e->next) {
+static void env_update(Env **env, const char *name, int val) {
+  for (Env *e = *env; e; e = e->next) {
     if (strcmp(e->name, name) == 0) {
       e->val = val;
       return;
@@ -157,26 +149,25 @@ static void env_update(const char *name, int val) {
   Env *e = malloc(sizeof(Env));
   e->name = strdup(name);
   e->val = val;
-  e->next = env;
-  env = e;
+  e->next = *env;
+  *env = e;
 }
 
-void env_print(void) {
-  Env *current_env = env;
-  while (current_env) {
-    printf("%s = %d\n", current_env->name, current_env->val);
-    current_env = current_env->next;
+void env_print(Env *env) {
+  Env *e = env;
+  while (e) {
+    printf("%s = %d\n", e->name, e->val);
+    e = e->next;
   }
 }
 
-
-static int eval_aexpr(ASTNode *node) {
+static int eval_aexpr(Env **env, ASTNode *node) {
   switch (node->type) {
     case NT_INT: return node->u.d_int.val;
-    case NT_VAR: return env_lookup(node->u.d_var.name);
+    case NT_VAR: return env_lookup(*env, node->u.d_var.name);
     case NT_AOP: {
-      int aexp1 = eval_aexpr(node->u.d_aop.aexp1);
-      int aexp2 = eval_aexpr(node->u.d_aop.aexp2);
+      int aexp1 = eval_aexpr(env, node->u.d_aop.aexp1);
+      int aexp2 = eval_aexpr(env, node->u.d_aop.aexp2);
       switch (node->u.d_aop.aop) {
         case AOP_ADD: return aexp1 + aexp2;
         case AOP_SUB: return aexp1 - aexp2;
@@ -189,21 +180,21 @@ static int eval_aexpr(ASTNode *node) {
   }
 }
 
-static int eval_bexpr(ASTNode *node) {
+static int eval_bexpr(Env **env, ASTNode *node) {
   switch (node->type) {
     case NT_BOP: {
-      int bexp1 = eval_bexpr(node->u.d_bop.bexp1);
-      int bexp2 = eval_bexpr(node->u.d_bop.bexp2);
+      int bexp1 = eval_bexpr(env, node->u.d_bop.bexp1);
+      int bexp2 = eval_bexpr(env, node->u.d_bop.bexp2);
       switch (node->u.d_bop.bop) {
         case BOP_AND: return bexp1 && bexp2;
         case BOP_OR:  return bexp1 || bexp2;
       }
     }
     case NT_NOT:
-      return !eval_bexpr(node->u.d_not.bexp);
+      return !eval_bexpr(env, node->u.d_not.bexp);
     case NT_ROP: {
-      int aexp1 = eval_aexpr(node->u.d_rop.aexp1);
-      int aexp2 = eval_aexpr(node->u.d_rop.aexp2);
+      int aexp1 = eval_aexpr(env, node->u.d_rop.aexp1);
+      int aexp2 = eval_aexpr(env, node->u.d_rop.aexp2);
       switch (node->u.d_rop.rop) {
         case ROP_EQ: return aexp1 == aexp2;
         case ROP_NE: return aexp1 != aexp2;
@@ -219,30 +210,30 @@ static int eval_bexpr(ASTNode *node) {
   }
 }
 
-void exec_stmt(ASTNode *node) {
+void exec_stmt(Env **env, ASTNode *node) {
   while (node) {
     switch (node->type) {
       case NT_SKIP:
         return;
       case NT_ASSIGN: {
         char *var = node->u.d_assign.var->u.d_var.name;
-        int val = eval_aexpr(node->u.d_assign.aexp);
-        env_update(var, val);
+        int val = eval_aexpr(env, node->u.d_assign.aexp);
+        env_update(env, var, val);
         return;
       }
       case NT_SEQ:
-        exec_stmt(node->u.d_seq.stm1);
-        exec_stmt(node->u.d_seq.stm2);
+        exec_stmt(env, node->u.d_seq.stm1);
+        exec_stmt(env, node->u.d_seq.stm2);
         return;
       case NT_IF:
-        if (eval_bexpr(node->u.d_if.bexp))
-          exec_stmt(node->u.d_if.stm1);
+        if (eval_bexpr(env, node->u.d_if.bexp))
+          exec_stmt(env, node->u.d_if.stm1);
         else
-          exec_stmt(node->u.d_if.stm2);
+          exec_stmt(env, node->u.d_if.stm2);
         return;
       case NT_WHILE:
-        while (eval_bexpr(node->u.d_while.bexp)) {
-          exec_stmt(node->u.d_while.stm);
+        while (eval_bexpr(env, node->u.d_while.bexp)) {
+          exec_stmt(env, node->u.d_while.stm);
         }
         return;
       default:
diff --git a/ast.h b/ast.h
index 7a58372..7dd9697 100644
--- a/ast.h
+++ b/ast.h
@@ -38,9 +38,15 @@ ASTNode *ast_bop(BOp bop, ASTNode *bexp1, ASTNode *bexp2);
 ASTNode *ast_not(ASTNode *bexp);
 ASTNode *ast_rop(ROp rop, ASTNode *aexp1, ASTNode *aexp2);
 
-void exec_stmt(ASTNode *node);
+typedef struct Env {
+  char *name;
+  int val;
+  struct Env *next;
+} Env;
+
+void exec_stmt(Env **env, ASTNode *node);
 void free_ast(ASTNode *node);
-void env_print(void);
+void env_print(Env *env);
 
 #endif
 
diff --git a/driver.c b/driver.c
index d89c412..6b0909e 100644
--- a/driver.c
+++ b/driver.c
@@ -22,8 +22,9 @@ int main(int argc, char **argv) {
     return EXIT_FAILURE;
   }
   
-  exec_stmt(ast_root);
-  env_print();
+  Env *env = NULL;
+  exec_stmt(&env, ast_root);
+  env_print(env);
   free_ast(ast_root);
   
   return EXIT_SUCCESS;