CRAWL Language Reference Manual Rajesh Venkataraman Amoghavarsha Ramappa rv2187 columbia edu ar2645 columbia edu Carter Adams carteradams gmail com 1 Lexical Conventions A CRAWL program is consists of a single translation unit stored in a file The file is written using the ASCII character set 1 1 Comments CRAWL comments begin with a character at the beginning of the line and are terminated at the end of the line 1 2 Whitespace CRAWL is a free form language Whitespace is ignored unless bounded by quotes on either side 1 3 Tokens Tokens fall into five major categories identifiers keywords constants operators and separators 1 3 1 Identifiers Identifiers begin with a letter or an underscore and are followed by any sequence of letters digits or underscores Two characters are considered equal if their ASCII values are equal Two identifiers are considered equal if all their characters match 1 3 2 Keywords The following identifiers are reserved as keywords and using them in any CRAWL program as a regular identifier will result in an error int float edge graph string while if else foreach in sizeof where 1 3 3 Constants Constants provide the CRAWL programmer to conveniently initialise each of the supported primitives Integer Constants An Integer constant consists of an optional plus sign or minus sign followed by a string of decimal digits 0 9 Floating point Constants A floating point constant is defined similar to the definition in the C language that is it consists of an optional plus sign or minus sign followed by an integer part of one or more digits This has to be followed by a decimal point or an exponent sign The decimal point might be followed by more digits The exponent is always followed by a positive or negative integer String Constants String constants consist of a sequence of characters surrounded by double quotes The quotes are not considered part of the string and the character is used to generate escape sequences If the constant has to contain the character literally one has to use the sequence The following escape sequences are recognised by CRAWL n newline t The horizontal tab 1 3 4 Operators Arithmetic operators The following arithmetic operators are supported by CRAWL and Their meanings are respectively those of addition subtraction multiplication division and remainder after division The operator can also be used as a unary operator to indicate the negativity of a number The binary operators operands must have have the same type and are used to mean the same thing as they do in the C language The associativities of these operators also follow those of the C language Collection operators CRAWL supports the operator to define collections The sign followed by a sequence of comma separated values terminated by a sign is construed to be a collection The operator is also supported to randomly access collection s elements Hence in order to access the ith element of a collection C one might use C i Boolean operators The following boolean operations are supported in CRAWL which respectively mean less than less than or equal to greater than greater than or equal to equal to and the negation of the boolean operation In addition CRAWL supports the and operators to mean boolean and and boolean or Sizeof The sizeof operator when used with strings returns their length and with integers and floats returns the value Behaviour of this operator when applied to Edges Graphs and Collections is explained later Precedence The precedence and associativities of the operators in CRAWL are identical to their counterparts in C To override this one might use parentheses 1 3 5 Separators and are used as separators in CRAWL The separator indicates end of executable statement 1 3 6 Scope The scope of an identifier begins at immediately after its definition and ends at the end of the block Blocks are delimited using the and separators 2 Types 2 1 Integers Floats and Strings Integers and Double precision floating point numbers are the only two numeric types supported by CRAWL Strings are sequences of ASCII characters 2 2 Collections CRAWL supports a basic collection type not very different from the array type in C It provides random access of elements and the elements are ordered in the collection according to the order that they were inserted While creating collections the size of the collection has to be specified Collections support the operator which allows the programmer to add a new element to the collection The sizeof operator can be used to get the number of elements in the collection 2 3 Edges In order to describe the connections in a graph CRAWL supports the edge data type An edge is composed of three parameters namely the 2 nodes that it connects and a weight associated with the two edges Edges literals are defined as a comma separated list of these 3 elements delimited by parentheses For example 1 2 red defines an edge between nodes 1 and 2 with weight red The operator applied to an edge returns the node that it is incident on and the returns the node that it is incident from On applying the sizeof operator to an edge the weight is returned 2 4 Graphs Graphs in CRAWL are defined just as a pair namely that of the number of nodes and a collection of edges Graph literals are of the form num of nodes edge collection Graphs also support the binary operator which returns a collection of edges going out from the given node For example g 3 returns a collection of edges going out from node number 3 Nodes are numbered from 0 to n 1 where n is the number of nodes in the Graph They also support the operator which returns a collection of edges incident on the specified node Using the sizeof keyword one can get the number of nodes in the Graph 3 Control Structures Loops and branching constructs foreach in where foreach is a keyword used to iterate over a collection Used in conjunction with the in operator it allows for obtaining the next element from the collection being iterated over The where keyword can be used to further limit the execution of this loop For example to find the sum of the elements in an integer collection where the value is greater than or equal to 2 one might write int num 0 int coll 10 1 2 3 foreach num in coll where num 2 sum num while while is a looping construct It tests a condition at the beginning of each iteration and executes the statements in the loop if the condition evaluates to be true The statements associated with the loop must be enclosed in braces if if is a
View Full Document
Unlocking...