Sumatra Basics. Ing. Petr Aubrecht

Transcription

1 Sumatra Basics Ing. Petr Aubrecht 12/4/2000

2 Abstract The main aim of this report is to describe basics of our empty language, Sumatra. Sumatra was initially developed for data transformation, depending on metadata information. We followed the possibility of expansion of a language in future, the easy, well-known grammar and natural use of project-dependent objects or functions. Keeping these goals in view we developed language similar to C (or Java). It has all common statements like cycles, conditional and compound statements. The core is programmed to be independent on compiler or system. The extensibility is achieved by so-called template files, which are designed for simple forming new objects and functions.

3 Contents 1 History 3 2 Implementation of Sumatra Definitions Features of Sumatra Language Variables Functions Objects Statements Structures Compound Statement Assignment Increment, Decrement Conditional Statement Cycles for while do break, continue exit Basic Types int double string datetime Basic Functions User Defined Types

4 4 Working Implementations PumpSumatra ASTSumatra Conclusion 14 2

5 Chapter 1 History During work on GOAL 1 project was created metadata repository, called AST. In this repository metadata of data sources are stored. These metadata are intended to serve for data transformation between different sources. At the moment metadata repository became able to embed structures of data sources (metadata) and access these sources, the language for data transformations became necessary. There were several possibilities: simple mapping is the simplest way. Means mapping one field to another, copying its value. Doesn t allow merge several fields into one. expressions are able to successfully solve mapping one line from one source to one line in other source. In order to implement expressions consisting from several source, there should be also integral references defined, a way of manipulating rows in non-dependent sources etc. interpreted language is a very powerful way. In programming language there is possible write any operation with more sources. The only trouble is a more complexity of a such program (opening sources, handling errors). We decided to choose this solution and we developed Sumatra. compiler is the fastest running solution. But it is highly dependent on hardware and operating system, aside from complex implementation. 1 INCO COPERNICUS GOAL (Geographical Information On-Line Analysis), see the Acknowledgment 3

6 During design phase we conclude the first two options are too restrictive. They don t allow us to describe more complex transformation than 1 line to 1 line. We decided to build up a interpreter for imperative 2 language. Its grammar was inspired by C and Java (from which the name is derived). During the Sumatra development the idea of the language have been generalized. We changed the idea of transformation language to a empty language. Empty means it has only several basic types and a set of application defined. Sumatra is intended to be used inside other applications enabling controlling of this application by scripts. The idea is shown at the figure 1.1. Script Application Script language 3 Internal objects Figure 1.1: Application with a scripting language The advantage of a chosen solution is in wide usability. Sumatra can be embedded generally into any application. We tried this approach in several Sumatra implementations and we developed a set of template files, intended for speeding up implementation of user defined objects. Using of metadata is shown in chapter Working Implementations. Today, a set of functions and objects is under development and are prepared to be reused in other implementations. 2 imperative language means directed by statements, ex. C++, Pascal, (in contrast to declarative languages like Prolog or Lisp) 4

7 Chapter 2 Implementation of Sumatra 2.1 Definitions The most important term in this context is implementation of Sumatra. It means a new version of Sumatra with user (implementor, application) defined types. Sumatra comes with a set of native types and implementation extend them with new ones, possibly with new functions. Better description is given in [1]. One of used terms in language part is overcast. Overcast means changing type of some expression to other one. For example, all numbers in Sumatra source is recognized as double type. Thus in int i=1;, there is double type (number 1) changed to int. 5

8 Chapter 3 Features of Sumatra Language Sumatra is inspired by C++ and Java languages. Therefore statements are written in the same fashion. Each statement is followed by a semicolon (;). Sumatra is case sensitive, i.e. for and For are two different terms. In Sumatra, there is a set of statements, described later. They all use only small letters (for,if). Comments are of two types. First type is block, having the beginning marked by /* and ended by */. The other type is so called line comment. It starts with // and ends with the end of line. Spaces, tabulators, new line characters and comments can be freely used. They only may not divide one term (e.g. name of variable or statement). Because Sumatra is intended to be a scripting languages, it doesn t support functions so far. 3.1 Variables Variables are determined by their name and has a type. Variables are defined by type name followed by a list of variables and terminated by s semicolon: int var1,var2; Variables can be set up during definition. An expression can be assigned to the variable writing a equal mark and the expression: int i=0; int one=1,two=one+1,three=one+two,four=two*two; 6

9 3.2 Functions A functions are called by their name and a set of arguments. Every function has a list of arguments (possibly empty) and their type, so every expression has to have an appropriate type. Message("hello"); 3.3 Objects A term object is here user for data type. Each type in Sumatra is an object. Objects can have data members and methods, accessible by a dot convention: datetime today; today.day = 1; today.addday(1); Objects can have in addition operators, mostly mathematical or string operations: string left="l",right="r"; Message(left+right); 3.4 Statements Structures 3.5 Compound Statement A set of statements can be grouped into one using braces: { } Message("hello world!"); exit; Compound statements are necessary in conditional statements and cycles at the place of one allowed statement. 7

10 3.6 Assignment Assignment consists from two parts delimited by equal mark. On the left side, there have to be an object able to accept value, most usually variables: i=1; On the right side there can be expression of an appropriate type the same type as on the left side. The only exception is if there exists a default overcast. Information about default overcasts can be obtained from a documentation of the concrete implementation. Basically, there are defined overcasts between int and double Increment, Decrement A special forms of assignment are increment and decrement. Increment is written using ++ and decrement using --. i++; y--; 3.7 Conditional Statement Conditional statement executes two different statements depending on a result of a condition. if(today="friday") Message("Have a nice weekend!"); else Message("Continue working!"); The else part is optional: if(today="friday") Message("Have a nice weekend!"); 8

11 3.8 Cycles A very important matter of each language are cycles. Sumatra implements all common types of cycles a fixed count cycle, a cycle with a condition on the beginning and one with condition at the end. In addition, Sumatra designs foreach cycle intended for simple usage of data source. All cycles use a condition. The type of the condition is int and becomes true if the expression is different from zero for A for cycle has four parts. First three parts are used for controlling of the cycle and the fourth is a command repeatedly executed. First part is executed once at the beginning, the second part a condition for cycling (i.e. a cycle stops when the condition becomes false), and the third part is executed every cycle. The most common usage is: for(i=0;i<10;i++) Message(IntToStr(i)); while A while cycle has a condition at the beginning: int i=0,start=clock(); while(clock()-start<1000) i++; do A do cycle has a condition at the end: int i=0,start=clock(); do() { Message("Wait and then press OK"); } while(clock()-start<1000); 9

12 3.8.4 break, continue The statements break and continue can be used only in body of cycle (using them out of cycle is a grammar error). break stops executing a cycle and continues with the next statement. In the example the first occurrence of a character is reported: for(i=0;i<str.len();i++) { if(str.get="a") { Message(" a has been found!"); break; } } continue stops executing the current (usually compound) command and continues executing the cycle. The example leaves all occurrences of a and replaces all others by b. for(i=0;i<str.len();i++) { if(str.get(i)="a") continue; str.set(i,"b"); } 3.9 exit There is a statement used for immediate termination of whole script, usually as a reaction to errorneous state. if(ok!=1) { Message("Error!"); exit; } 10

13 3.10 Basic Types The core of Sumatra provides several basic types. These types aren t necessary (can be defined differently), but these types are general and usually need no changes. Numeric basic types (int and double) follows C++ equivalents. Type string is derived from STL library. Type datetime uses our original code for date time processing. A definitions of int, double, and string are required. These types are used by core. A description of each with explanation follows. Implementation of basic types simplifies start of new implementations. It can include only one user defined type or function (usually Message for testing of running Sumatra) and run simple Sumatra scripts int Type int uses C++ int in background. Its size in bits depends on compiler used for compiling of Sumatra core. For this type are defined usual mathematical operations. Most Sumatra statements uses condition, which is of type int double Type double is similar to int. Both types have default overcasts for mutual conversions. All numbers found in Sumatra core are recognized as double string Type string is intended for simplified manipulation with strings. Strings can be simply merged, there is access to individual characters (as ints). In Sumatra scripts strings are written using " characters at the beginning and end. 11

14 In strings are often used control character, mostly END-OF-LINE. These characters are written as backslash (\) and a specification character: \\ means \ itself \n is a carriage return character (ASCII code 13) \r is a line feed character (ASCII code 10) \t is a tabulator character \ is a double quote character (not an end of string) datetime Date and time are very hard to handle, especially together. Therefore Sumatra dispose of a such type for simple work with time complexly. This type offers mathematical operations (sum and difference), comparisons, formatting, day in week, week number, adding days and other features. A datetime type is intended for simplified database data handling, where the date/time fields are often hard to manipulate Basic Functions In Sumatra there is a set of help functions. A pair of functions IntToStr and StrToInt are designed to transform between int and string types. Conversion of double is a bit richer. It uses a FormatNumber function with a possibility to add a format string. During execution this string is inserted between % and lf in C function sprintf. This allows normal C formatting. There is a function returning the current date and time Now() User Defined Types Each implementation of Sumatra has to add its own types and/or functions. At least, a Message(string) is desired for comfortable work. 12

15 Chapter 4 Working Implementations There are two exemplary implementation used for Sumatra capability demonstration. 4.1 PumpSumatra A PumpSumatra implementation has included objects copying database objects from Borland C++ Builder 5. These objects are TDatabase, TQuery and TField. Sumatra objects have the most important data members and methods from the Borland s ones. With this implementation a transformation of data from A2 application of a GOAL project ([2]) has been done. 4.2 ASTSumatra On demand of a GOAL project there is a need of utilization of metadata stored in metadata repository (AST tree). The metadata repository provides both metadata (description of data structure) and data access. This feature is used in ASTSumatra for source independent data processing. Once data are described in metadata repository, ASTSumatra can create a data object and access it abstractedly from its type. 13

16 Chapter 5 Conclusion The state of the art of Sumatra development is satisfactory. It is able to quickly create a proxy (controlled by script in Sumatra) objects and control the native objects (application s ones). Language capabilities are sufficient for transformation. There are two points to improve: foreach cycle and functions. 14

17 Acknowledgment The research of Sumatra has been carried out under the support of the INCO COPERNICUS GOAL (Geographical Information On-Line Analysis) and under the support of the supporting grant of MSMT CR OK

18 Bibliography [1] Petr Aubrecht. Tutorial of Sumatra Embedding. Technical report GL 101/00 1, Czech Technical University, Department of Cybernetics, Technická 2, Prague 6, October [2] Kouba Z. Miksovsky P. Application a2 specification. Technical report TR11, INCO COPERNICUS GOAL, Czech Technical University, Department of Cybernetics, Technická 2, Prague 6,