The BATS Language Reference Manual Behrooz Badii Team Leader Tanya Shtemberg Aleksandr Borovinskiy Sui Sum Wong October 28 2003 Introduction The BATS language a geometric figure drawing language was designed to be simple to use Through its simplicity complex figures can be drawn using complex algorithms The language also includes loops conditional statements and functions to modularize a programmer s language These pieces of block structured programming are essential for effectively representing geometric algorithms in an understandable format And since this is a drawing language the choice of declaring assigning and using lines as will be seen will make drawing vastly easier BATS will use an interpreter that interprets BATS code into the target language Java Syntax Grammar notation This language reference manual uses a pseudo ANTLR language to represent the grammar of BATS Grammars are clearly divided from paragraphing and text to show the grammar exactly Alternatives are separated by the character Nonterminals can be placed in an optional set of parentheses but they are also always italicized Literals or terminals are placed in single quotes i e 1 e A set of literals such as the alphabetic set can be placed in parentheses where the first quoted literal is followed by two periods which is followed by the last literal of the set in single quotes Optional expressions are placed in parentheses followed by the questions mark character Iteration is placed in parentheses followed by either the kleene star which means that the parenthesized literals and or syntactic categories can be matched zero or more times or the plus character which means that the parenthesized literals and or syntactic categories must be matched at least once Epsilon is represented as nothing So in the grammar Yourname Name A Z Name Name A Z a z Yourname is the starting symbol The first name or Name is a syntactic subcategory that expands to one uppercase letter followed by any number of lowercase letters After Name the middle initial is just an optional single uppercase letter The last name is just Name reiterated to match a last name Lexical conventions The following are the tokens found in this language identifiers keywords constants operators and separators Separators Blanks the whitespace tabs new lines carriage returns and comments are ignored in token creation other than to serve the purpose of separating tokens The input stream which is a file containing BATS programs is parsed so that each token is taken to include the longest string of characters which could possibly constitute a token This means the parser will keep adding to the token until it hits a whitespace a tab a new line a carriage return or a comment Comments The question mark character introduces a comment which terminates with a new line Another convention for comments is starting a comment with the characters and ending the comment with Identifiers Names An identifier is a sequence of letters and digits where the first character must be alphabetic The underscore is counted as a letter Upper and lower case letters are considered different The following is the grammar for an identifier Identifier A Z a z A Z a z 0 9 These are some examples of identifier names hello hello1 hi3 I AM A VARIABLE The following cannot be identifiers 1joe thr ee b leach Keywords Keywords are reserved words that aid the programmer in creating an understandable program that the compiler will accept These keywords are used for things such as looping conditional statements and type declarations To make them easier to see in a BATS text they all start with a capital letter No identifier can have a name identical to the following keywords Double To Start WhileEnd Color Int Draw Terminate ForEnd Then Boolean Call While IfEnd Line Function For True Point Begin If False From End Else Do Constants There are three different types of constants in the BATS language integer constants double constants and Boolean constants These three are defined as follows Integers An integer consists of a sequence of ASCII character 1 to 9 and that sequence of ASCII characters represents its real number value For example the real number value equivalent of the sequence 123 is 123 or one hundred twenty three The following is the grammar composing an integer constant Integer Digit Digit 0 9 Doubles A double constant is a sequence of digits followed by a mandatory ASCII decimal or dot which is then followed by another sequence of digits which is then followed by an optional exponent The exponent part of a double constant consists of an upper or lower case e followed by an optional positive or negative sign followed by another sequence of digits The following is the grammar composing a double constant Double Digit Digit Exponent Exponent e E Digit Notice the mandatory digit in front of the decimal This makes the double constant found in the BATS language similar to the double values in a regular hand held calculator For example the number 067 is represented as 0 067 in the BATS language which is similar to the representation of that number in a calculator The following are examples double constants 145 167 145 167 E 26 0 12 e 13 The following are examples of input that can t be a double constant 145 167 145 e 12 Booleans There are only two Boolean constants in the BATS language and they are True and False representing the logical values of true and false respectively The following is the grammar for a Boolean constant Boolean True False What an Identifier Stands For An identifier can stand for another identifier a constant or a more complex set of constants The attributes of an identifier are the storage class and its type The storage class of an identifier defines the scope of an identifier that is to say how long and where the identifier exists through the running of a program Its type is the type of constant or complex set of constants it stands for Currently there are two storage classes an identifier can choose from to have The first storage class is global The identifier exists inside and outside all functions until the program has terminated A global identifier is declared outside all functions in the global arena The second storage class is functional Here the identifier exists inside only a specific function and disappears when the function returns to its caller The type of an identifier can be of the following simple constants Integer Integers Int are represented by an actual integer
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