Parsing exprs, enum_decls, Introduce intern table, symbol table

expr.h

@@ -0,0 +1,50 @@
+#pragma once
+typedef struct Expr Expr;
+
+typedef enum Expr_Kind{
+  EK_None,
+  EK_Atom,
+  EK_Unary, 
+  EK_Binary, 
+  EK_Ternary,
+  EK_Cast,
+  EK_List, 
+  EK_Call, 
+  EK_Index,
+} Expr_Kind;
+
+struct Expr {
+  Expr_Kind kind;
+  Token *token;
+  Expr  *next;
+  union {
+    struct {
+      Type *type;
+      Expr* expr;
+    } cast;
+    struct {
+      Expr *first;
+      Expr *last;
+    } list;
+    struct {
+      Expr *atom;
+      Expr *list;
+    } call;
+    struct {
+      Expr *atom;
+      Expr *index;
+    } index;
+    struct {
+      Expr* expr;
+    } unary;
+    struct {
+      Expr* left;
+      Expr* right;
+    } binary;
+    struct {
+      Expr* cond;
+      Expr* on_true;
+      Expr* on_false;
+    } ternary;
+  };
+};