处理inger中的各种数据类型和标识符，如BOOL, unsigned long, float, char*,标识符等
typedef union
{
    unsigned long  uintvalue;
    BOOL    boolvalue;
    char   *stringvalue;
    char    charvalue;
    float   floatvalue;
    char   *identifier;
} Tokenvalue;

树节点结构(注意：树节点和抽象语法树节点是不同的)：
typedef struct TreeNode
{
    void            *data;
    int              screenX;
    struct TreeNode *parent;
    List            *children; //一系列孩子
} TreeNode;

抽象语法树节点结构：
typedef struct AstNode
{
    int         id;  //表示节点的类型，如while节点，module节点
    Tokenvalue  val;
    Type       *type;
    int         lineno;
} AstNode;

抽象语法树的AstNode作为TreeNode的data成员保存，参考如下函数：
//参数id表示节点名，如：NODE_MODULE,NODE_GLOBAL等见nodenames.h
TreeNode *CreateAstNode( int id, int lineno )
{
    TreeNode *treeNode;
    AstNode *astNode;

    astNode = (AstNode *) MallocEx( sizeof( AstNode ) );
    astNode->id = id;
    astNode->lineno = lineno;
    astNode->val.uintvalue = 0;
    astNode->type = NULL;
    treeNode = CreateTreeNode( astNode );

    return( treeNode );
}
或者：
TreeNode *CreateAstNodeVal( int id, Tokenvalue val, int lineno )
{
    TreeNode *treeNode;
    AstNode *astNode;

    astNode = (AstNode *) MallocEx( sizeof( AstNode ) );
    astNode->id = id;
    astNode->lineno = lineno;
    astNode->val = val;
    astNode->type = NULL;
    treeNode = CreateTreeNode( astNode );

    return( treeNode );
}

//抽象语法树节点名
enum NodeNames
{
    NODE_MODULE = 0,
    NODE_START,
    NODE_EXTERN,
    NODE_GLOBAL,
    NODE_FUNCTION,
    NODE_FUNCTIONHEADER,
    NODE_MODIFIERS,
    NODE_PARAMLIST,
    NODE_PARAMBLOCK,
    NODE_PARAM,
    NODE_RETURNTYPE,
    NODE_DIMENSION,
    NODE_DIMENSIONBLOCK,
    NODE_BLOCK,
    NODE_STATEMENT,
    NODE_SWITCH,
    NODE_CASES,
    NODE_CASE,
    NODE_WHILE,
    NODE_GOTO,
    NODE_LABEL,
    NODE_IF,
    NODE_IDENT,
    NODE_RETURN,
    NODE_CONTINUE,
    NODE_BREAK,
    NODE_DECLBLOCK,
    NODE_DECLARATION,
    NODE_INITIALIZER,
    NODE_INDEXBLOCK,
    NODE_REFERENCE,
    NODE_INDEX,
    NODE_EXPRESSION,
    NODE_LOGICAL_OR,
    NODE_LOGICAL_AND,
    NODE_BITWISE_OR,
    NODE_BITWISE_XOR,
    NODE_BITWISE_AND,
    NODE_EQUAL,
    NODE_NOTEQUAL,
    NODE_GREATER,
    NODE_GREATEREQUAL,
    NODE_LESS,
    NODE_LESSEQUAL,
    NODE_BITWISE_LSHIFT,
    NODE_BITWISE_RSHIFT,
    NODE_ASSIGN,
    NODE_BINARY_ADD,
    NODE_BINARY_SUBTRACT,
    NODE_UNARY_ADD,
    NODE_UNARY_SUBTRACT,
    NODE_MULTIPLY,
    NODE_DIVIDE,
    NODE_MODULUS,
    NODE_BITWISE_COMPLEMENT,
    NODE_ADDRESS,
    NODE_DEREFERENCE,
    NODE_NOT,
    NODE_APPLICATION,
    NODE_INDEXER,
    NODE_ARGUMENTS,
    NODE_FACTOR,

    NODE_BOOL,
    NODE_CHAR,
    NODE_FLOAT,
    NODE_INT,
    NODE_UNTYPED,
    NODE_VOID,

    NODE_LIT_BOOL,
    NODE_LIT_CHAR,
    NODE_LIT_FLOAT,
    NODE_LIT_INT,
    NODE_LIT_STRING,
    NODE_LIT_IDENTIFIER,

    NODE_INT_TO_FLOAT,
    NODE_CHAR_TO_INT,
    NODE_CHAR_TO_FLOAT,

    NODE_UNKNOWN = -1
};

输出抽象语法树：
/*
 * PRINTING ROUTINES
 */
void PrintAst( TreeNode *source )
{
    PrintTree( source, GetAstNodeData, 4 );
}
PrintTree的实现如下，这里传递的参数levels等于4
void PrintTree( TreeNode *source, DataFunction dataFunction, int levels )
{
    int printDepth = 0;
    BOOL loop;
    char *str;
    int i;

    /* TODO: We're going to have to make a new macro.
     * Don't use DEBUG for this.
     */
    DEBUG( "Called\n" );

    /* If tree is empty, abort. */
    if( source == NULL )
    {
        return;
    }

    /* Walk through tree to determine x-offsets for
     * each node.
     */
    LayoutTree( source, LEFT_OFFSET );

/* Print nodes. */
依次通过调用函数指针dataFunction所指向的函数(实际上是函数GetAstNodeData)
来输出每个节点的节点名，节点的token的值，类型名，以及行号，参考下面的GetAstNodeData函数

    for( i = 0; i < levels; i++ )
    {
        str = dataFunction( source, i );
        PrintChars( source->screenX - strlen( str ) / 2, ' ' );
        printf( "%s\n", str );
    }
    PrintChars( source->screenX, ' ' );
    printf( "%c", VERTBAR );

    printDepth = 0;
    do
    {
        currentX = 0;
        printf("\n");
        PrintNode( source, 0, printDepth, 0, dataFunction, 0 );
        currentX = 0;
        printf("\n");
        PrintNode( source, 0, printDepth, 1, dataFunction, 0 );
        currentX = 0;
        printf("\n");
        for( i = 0; i < levels; i++ )
        {
            PrintNode( source, 0, printDepth, 2, dataFunction, i );
            currentX = 0;
            printf("\n");
        }
        loop = PrintNode( source, 0, printDepth, 3, dataFunction, 0 );
        printDepth++;
    }
    while( loop );
}

添加一个孩子的操作只需要将新节点插入到孩子链表尾部即可
void AddTreeChild( TreeNode *parentnode, TreeNode *node )
{
    /* Do not act on an empty node. */
    if( node == NULL ) return;

    /* If the tree is empty, add the first root node. */
    if( parentnode == NULL )
    {
       node->parent = NULL;
    }
    else
    /* Tree is not empty. Add the new node to [parentnode]'s
     * children list. */
    {
       node->parent = parentnode;

       ListAppend( parentnode->children, node );
    }
}

而RemoveAstNode则删除整个子树
/* Remove node [node] from ast. The node contents
 * and its children get deleted.
 *
 * Pre:  [node] is not NULL.
 */
void RemoveAstNode( TreeNode *node );

inger编译流程：
1. 预处理，关键函数为Preprocess
2. 语法分析，构建抽象语法树，关键函数Parse，Parse也是构造抽象语法树的入口函数，如果语法分析没有发现错误则跳到第3步
3. 根据抽象语法树来建立符号表关键函数为CreateSymbolTable( ast );
4. 语义分析，关键函数：
a) CheckLeftValues( ast );
b) CheckArgCount( ast );
c) CheckSwitchStatements( ast );
d) CheckFunctionReturns( ast );

5.  根据抽象语法树生成代码，关键函数GenerateCode( ast );