Programming Languages and Translators COMS W4115 Prof Stephen Edwards Summer 2008 VINL VINL Is Not Logo Language Reference Manual Yang Cao June 19 2008 Table of Contents 1 Introduction 2 2 Lexical Conventions 2 2 1 Tokens 2 2 2 Comments 2 2 3 Identifiers 2 2 4 Keywords 2 2 5 Floating Constants 2 2 6 String 2 2 7 Other Tokens 3 3 Types 3 3 1 decimal 3 3 2 String 3 3 3 boolean 3 3 4 void 3 4 Expressions 3 4 1 Primary Expressions 3 a identifiers 3 b constants 3 c strings 4 d Function Calls 4 4 2 Operators 4 a Multiplicative Operators 4 b Additive Operators 4 c Relational Operators 4 d Logical AND Operator 4 e Logical OR Operator 4 4 3 Assignment Expressions 4 5 Statements 5 5 1 Expression Statement 5 5 2 Selection Statement 5 5 3 Iteration Statement 5 5 4 Keyword statement 5 6 Scope 6 1 Introduction This language manual describes the VINL VINL is Not Logo language which is designed based on the popular C programming language syntactically and Logo programming language functionally 2 Lexical Conventions 2 1 Tokens There are six classes of tokens just as in C identifiers keywords constants strings operators and other separators White spaces consists of space tab and new line and are separators of tokens 2 2 Comments Comments starts with and terminates with end of line 2 3 Identifiers An identifier is a sequence of letters digits and underscores Identifiers can not start with a digit Identifiers are case sensitive 2 4 Keywords The following identifiers are reserved for use as keywords and may not be defined as variable names or function names 2 5 boolean break continue decimal for forward if pendown penup right void while else print Floating Constants Floating constants consists of an mandatory integer part an optional decimal point and an optional fraction part 2 6 String String literals are sequence of characters surrounded by double quotes A double quote inside the surrounding double quotes is escaped by backward slash A backward slash inside the double quotes is escaped by backward slash as well 2 7 Other Tokens Other tokens used in VINL including 3 Types VINL is statically typed All variables must be declared as either a decimal a string or a boolean Function declaration must specify a return type There will be no explicit nor implicit casting in VINL between boolean and decimals When the concatenation operation is performed on strings and decimal boolean the other type will be automatically converted to a string literal VINL follows Java conversion rule a decimal will become a string with digits representing its value and boolean will be either true or false The following is a list of the build in types 3 1 decimal A floating constant The memory storage size of decimal type is not specified In this implementation it will be 64bit value Behaviors on operations on a decimal resulting in overflow divide check and other exceptions are also not specified 3 2 String string of characters 3 3 boolean Either true or false 3 4 void Denotes nothingness One cannot create a variable of type void Used only in function declaration to show the function does not return any value 4 Expressions 4 1 Primary Expressions Primary expressions include identifiers constants strings function calls and expressions in parentheses a identifiers identifiers are lvalues and are evaluated to values stored in this memory space b constants constants are evaluated to itself c strings strings are evaluated to itself d Function Calls A function call consists of a identifier declared as a function followed by optional white space characters followed by a list of arguments surrounded by and 4 2 Operators The operators are listed by precedence highest to lowest they take primary expressions as operands a Multiplicative Operators and group left to right Only defined for decimal type constants and identifiers b Additive Operators and group left to right is only defined for decimal type constants and identifiers is defined for both string and decimals When one of the operands is string literal is defined as the concatenation operation c Relational Operators can be used to compare two decimals and they yield boolean values Those operators can not be chained e g a b c since boolean c is not allowed d Logical AND Operator group left to right and can be used in between two boolean expressions It yield boolean values It evaluates to true if and only if both boolean expressions are true e Logical OR Operator group left to right and can be used in between two boolean expressions It yield boolean values It evaluates to true if and only if at least one of the operands is true 4 3 Assignment Expressions There is only one assignment operator and it groups right to left It requires a type matching identifier on the left side of the operator The value of the expression on th right of the operator will be stored in the left identifier 5 Statements Statements are executed in sequence unless otherwise noted They do not have values and are executed for their effects Multiple statements maybe grouped together by and in that case they are treated as if they are a single statement 5 1 Expression Statement Expression statements have the form expression stmt expression All effects of the expression is completed before the next statement is executed A empty expression statement is a null statement and is often used for grouping related statements 5 2 Selection Statement Selection statements have the form selection stmt if expression statement if expression statement else statement The else groups with the closest else less if 5 3 Iteration Statement Iteration statements have the form iteration stmt while expression statement for expression expression expression statement The while loop stops if and only if the expression evaluates to false The for loop is equivalent to the following while loop initialization first optional expression while expression second optional expression statement post action third optional expression The keyword break and continue may only appear in the statement inside a loop body Break will stop the execution of the inner most loop immediately continue will stop the current iteration of the inner most loop and starts next iteration of this loop immediately 5 4 Keyword statement Keyword statements have the form keyword stmt forward decimal right decimal print string forward and right will impact the turtle while print will print to the stdout Print will have no effect on the turtle graph it should be used as a
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