Implement alias - a faster typedef

include/Defs.h

@@ -253,7 +253,8 @@ enum DataTypes {
 
     DAT_STRUCT = 80,     // Struct Data
     DAT_UNION,           // Union Data
-    DAT_ENUM = -1,            // Enum Data
+    DAT_ENUM,            // Enum Data
+    DAT_ALIAS,           // Alias Definition
 };
 
 /*
@@ -359,6 +360,10 @@ struct SymbolTableEntry* BeginCompositeDeclaration(int Type);
 
 void BeginEnumDeclaration();
 
+int ReadAlias(struct SymbolTableEntry** Composite);
+
+int ParseAlias(char* Name, struct SymbolTableEntry** Composite);
+
 struct ASTNode* GetExpressionList();
 
 struct ASTNode* CallFunction();
@@ -396,6 +401,8 @@ struct SymbolTableEntry* FindGlobal(char* Symbol);
 
 struct SymbolTableEntry* FindStruct(char* Symbol);
 
+struct SymbolTableEntry* FindAlias(char* Symbol);
+
 struct SymbolTableEntry* FindEnum(char* Symbol);
 
 struct SymbolTableEntry* FindEnumMember(char* Symbol);

src/Parser.c

@@ -135,8 +135,7 @@ struct ASTNode* ConstructASTLeaf(int Operation, int Type, struct SymbolTableEntr
  * @param IntValue: The integer value encoded by this Node, if applicable.
  * @return a newly constructed AST Node
  */
-struct ASTNode*
-ConstructASTBranch(int Operation, int Type, struct ASTNode* Left, struct SymbolTableEntry* Symbol, int IntValue) {
+struct ASTNode* ConstructASTBranch(int Operation, int Type, struct ASTNode* Left, struct SymbolTableEntry* Symbol, int IntValue) {
     return ConstructASTNode(Operation, Type, Left, NULL, NULL, Symbol, IntValue);
 }
 
@@ -159,6 +158,64 @@ int ParseTokenToOperation(int Token) {
     DieDecimal("ParseToken: Unknown token", Token);
 }
 
+/*
+ * The "alias" keyword allows one to create a new keyword that is accepted in lieu of another (or a chain of another)
+ * It does this by reading in sequence:
+ *  * The "alias" keyword
+ *  * The thing to alias (any valid primary type)
+ *  * The new name
+ *
+ * They are stored in a separate symbol table and can be used anywhere the original is valid.
+ */
+int ReadAlias(struct SymbolTableEntry** Composite) {
+    int Type;
+
+    Tokenise();
+
+    Type = ParseOptionalPointer(Composite);
+
+    if (FindAlias(CurrentIdentifier) != NULL)
+        DieMessage("Redefinition of type", CurrentIdentifier);
+
+    AddSymbol(CurrentIdentifier, Type, ST_VAR, SC_ALIAS, 0, 0, *Composite);
+    Tokenise();
+
+    return Type;
+}
+
+/**
+ * When using an alias, we need to lookup the name (possibly recursively) to check whether it is a valid alias.
+ * If so, we need to know what it is an alias of.
+ * Once we have resolved what it finally means, we return the type.
+ * @param Name The name of the (initial) alias to check
+ * @param Composite A pointer to the composite element we should fill in.
+ * @return The aliased type.
+ */
+int ParseAlias(char* Name, struct SymbolTableEntry** Composite) {
+    struct SymbolTableEntry* Type = NULL, *RootType = NULL;
+
+    // Ensure the first-round alias exists
+    Type = FindAlias(Name);
+    if (Type == NULL)
+        DieMessage("Unknown alias", Name);
+
+    // Loop on the alias for as long as it continues to exist.
+    while (true) {
+        if (Type->CompositeType == NULL)
+            break;
+
+        RootType = FindAlias(Type->CompositeType->Name);
+        if (RootType == NULL)
+            break;
+        Type = RootType;
+    }
+
+    Tokenise();
+    *Composite = Type->CompositeType;
+    return Type->Type;
+
+}
+
 /*
  * Primary expressions may be any one of:
  *  * A terminal integer literal
@@ -215,7 +272,7 @@ struct ASTNode* ParsePrimary(void) {
  *  the order of operations is upheld, that the precedence of the prior
  *  iteration is considered, and that every error is handled.
  * 
- * This is where all of the right-associative statements are folded, where
+ * This is where all the right-associative statements are folded, where
  *  type mismatches and widening are handled properly, and that all parsing 
  *   is over by the time the end tokens ") } ] ;" are encountered.
  * 
@@ -534,7 +591,7 @@ void ParseGlobals() {
 
         // Structs are parsed fully in ParseOptionalPointer
         // TODO: FIX THAT!!
-        if ((Type == DAT_STRUCT || Type == DAT_UNION || Type == DAT_ENUM) && CurrentToken.type == LI_SEMIC) {
+        if ((Type == DAT_STRUCT || Type == DAT_UNION || Type == DAT_ENUM || Type == DAT_ALIAS) && CurrentToken.type == LI_SEMIC) {
             Tokenise();
             continue;
         }

src/Pointers.c

@@ -92,9 +92,13 @@ int ParseOptionalPointer(struct SymbolTableEntry** Composite) {
             Type = RET_LONG;
             Tokenise();
             break;
-        case KW_STRUCT:
-            Type = DAT_STRUCT;
-            *Composite = BeginCompositeDeclaration(Type);
+        case TY_IDENTIFIER:
+            Type = ParseAlias(CurrentIdentifier, Composite);
+            break;
+        case KW_ALIAS:
+            Type = ReadAlias(Composite);
+            if (CurrentToken.type == LI_SEMIC)
+                Type = DAT_ALIAS;
             break;
         case KW_ENUM:
             Type = RET_INT;
@@ -102,6 +106,10 @@ int ParseOptionalPointer(struct SymbolTableEntry** Composite) {
             if (CurrentToken.type == LI_SEMIC)
                 Type = DAT_ENUM;
             break;
+        case KW_STRUCT:
+            Type = DAT_STRUCT;
+            *Composite = BeginCompositeDeclaration(Type);
+            break;
         case KW_UNION:
             Type = DAT_UNION;
             *Composite = BeginCompositeDeclaration(Type);

src/Symbols.c

@@ -143,6 +143,17 @@ struct SymbolTableEntry* FindEnumMember(char* Symbol) {
     return SearchList(Symbol, EnumMembers);
 }
 
+/*
+ * An override for FindSymbol.
+ * Searches only the defined enum members.
+ *  @param Symbol: The string name of the symbol to search for.
+ *  @return a pointer to the node if found, else NULL
+ *
+ */
+struct SymbolTableEntry* FindAlias(char* Symbol) {
+    return SearchList(Symbol, Types);
+}
+
 /*
  * An override for FindSymbol.
  * Searches only the defined Unions.
@@ -257,6 +268,9 @@ struct SymbolTableEntry* AddSymbol(char* Name, int Type, int Structure, int Stor
         case SC_ENUM:
             AppendSymbol(&Enums, &EnumsEnd, Node);
             break;
+        case SC_ALIAS:
+            AppendSymbol(&Types, &TypesEnd, Node);
+            break;
         case SC_ENUMENTRY:
             AppendSymbol(&EnumMembers, &EnumMembersEnd, Node);
             break;

tests/alias.er

@@ -0,0 +1,29 @@
+int :: printf(char* format);
+
+alias int water;
+water drink;
+
+struct fruit {
+    int x,
+    int y
+};
+
+alias struct fruit basket;
+basket food;
+
+alias basket shop;
+shop market;
+
+int :: main() {
+    drink = 5;
+    printf("%d\n", drink);
+
+    food.x = 10;
+    food.y = 66;
+    printf("%d\n", food.y);
+
+    market.y = 150;
+    printf("%d\n", market.y);
+
+    return (0);
+}