1 files changed, 117 insertions, 0 deletions
diff --git a/src/interpreter.c b/src/interpreter.c
new file mode 100644
index 0000000..4d1f8f9
--- /dev/null
+++ b/src/interpreter.c
@@ -0,0 +1,117 @@
+#include "interpreter.h"
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+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;
+    }
+  }
+  Env *e = malloc(sizeof(Env));
+  e->name = strdup(name);
+  e->val = val;
+  e->next = *env;
+  *env = e;
+}
+
+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;
+  }
+  env_update(env, name, 0);
+  return env_lookup(env, name);
+}
+
+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(Env **env, ASTNode *node) {
+  switch (node->type) {
+    case NT_INT: return node->u.d_int.val;
+    case NT_VAR: return env_lookup(env, node->u.d_var.name);
+    case NT_AOP: {
+      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;
+        case AOP_MUL: return aexp1 * aexp2;
+      }
+    }
+    default:
+      fprintf(stderr, "Bad aexpr node %d\n", node->type);
+      exit(EXIT_FAILURE);
+  }
+}
+
+static int eval_bexpr(Env **env, ASTNode *node) {
+  switch (node->type) {
+    case NT_BOP: {
+      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(env, node->u.d_not.bexp);
+    case NT_ROP: {
+      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;
+        case ROP_LT: return aexp1 < aexp2;
+        case ROP_LE: return aexp1 <= aexp2;
+        case ROP_GT: return aexp1 > aexp2;
+        case ROP_GE: return aexp1 >= aexp2;
+      }
+    }
+    default:
+      fprintf(stderr, "Bad bexpr node %d\n", node->type);
+      exit(EXIT_FAILURE);
+  }
+}
+
+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(env, node->u.d_assign.aexp);
+        env_update(env, var, val);
+        return;
+      }
+      case NT_SEQ:
+        exec_stmt(env, node->u.d_seq.stm1);
+        exec_stmt(env, node->u.d_seq.stm2);
+        return;
+      case NT_IF:
+        if (eval_bexpr(env, node->u.d_if.bexp))
+          exec_stmt(env, node->u.d_if.stm1);
+        else
+          exec_stmt(env, node->u.d_if.stm2);
+        return;
+      case NT_WHILE:
+        while (eval_bexpr(env, node->u.d_while.bexp)) {
+          exec_stmt(env, node->u.d_while.stm);
+        }
+        return;
+      default:
+        fprintf(stderr, "Bad stmt node %d\n", node->type);
+        exit(EXIT_FAILURE);
+    }
+  }
+}