编译原理 类型检查新.pptVIP

类型检查 ;类型表达式;函数与指针的类型表达式: Some languages allows functions to return an object of arbitrary type, e.g. LISP: (integer ? integer) ? (integer ? integer) 类型图 (tree or DAG) ;静态与动态的数据类型检查;Specification of a simple checker ;Type Checking: expressions;Type Checking: statements;Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.;Type Checking: functions;Equivalence of Type Expression;Algorithm for testing structural equivalence (type of constructor: arrays, products, pointers and functions): Type graph notation can be sometime expansive; we can use some code for representation like a sequence of bits ;Potential ambiguities appears when we give name to type expressions and the names are used in subsequent expression. We must verify if the name for expression stand for itself or it is an abbreviation for another expression. In some languages types can be given names. E.g: The Pascal language doesn’t define the term “identical type” When names are allowed in type expressions, two notions of equivalence of type expression arise: name equivalence (each name is viewed as distinct type) structural equivalence (names are replaced by the expression that they define – substitutions) ; Some implementation creates a fresh name every time when a type expression appears in a variable declaration.The declaration is treated as: ;With this representation, two type expressions are equivalent if they are represented by the same node in the type graph.;Types Representations: cycles;C language avoids cycles in type graphs using structural equivalence for all types except records C uses the keyword struct instead of record and the name cell is part of the type of the record. ;Type Conversions;Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.;Overloading of functions and operators;It is not always possible to resolve overloading by operator identification