Learning Language Reference Manual George Liao gkl2104 Joseanibal Colon Ramos jc2373 Stephen Robinson sar2120 Huabiao Xu hx2104 1 A Introduction Learning Language is a programming language designed to be accessible to students prior to entering high school Students at this age traditionally have no exposure to computer programming despite the fact that many of them have the maturity and education to write procedural logic For these students existing programming languages can be overwhelming due to their abstract syntax and the difficulty of implementing I O operations To that end the language is designed with the needs and abilities of 10 14 year old children in mind B Lexical Conventions B1 Comments The character introduces a comment which terminates at the next newline Comments do not occur within string literals B2 Identifiers An identifier is a sequence of letters and digits and underscores The first character must be a letter Upper and lower case letters are the same Identifiers may have any length B3 Keywords The following identifiers are reserved for use as keywords and may not be used otherwise string number fraction repeat If then read return function until displayline ifnot end readline called listof display end times open B4 Constants There are several kinds of constants Constant 2 Number constant String constant Fraction constant List constant Number Constant A number constant consists of a sequence of digits which are taken to be an integer in decimal base The sequence is optionally preceded by a for negative String Constant A string constant is a sequence of one or more characters enclosed in double quotes as in foobar In order to represent the character newlines and certain other characters the following escape sequences may be used Newline n Backslash Double quote Fraction Constant A fraction constant is two numbers separated by List Constant A list constant is a comma separated sequence of number fraction or string constants surrounded by braces Example 1 2 7 C Basic Types There are three basic types of variables in Learning Language They are number fraction and string The number type is a 32bit integer The fraction type is two 32 bit integers a numerator and a denominator The string type is a dynamically allocated array of characters The programmer does not need to specify the size of the string There is one derived type in Learning Language It is the list Lists can be of one of the three basic variable types or of another list Memory is dynamically allocated to the list as needed Users do not need to specify the size of their list D Conversions There is only one case where conversions occur in Learning Language For binary arithmetic operators if one operand is a number and the other a fraction then the number is promoted to a fraction 3 E Expressions E 1 Primary Expressions Primary expressions are identifiers constants strings or expressions in parenthesis Primary expression Identifier Constant String expression E 2 Postfix Operators The operators in postfix expressions group left to right Postfix expression Primary expression Postfix expression expression Postfix expression argument expression list Postfix expression Argument expression list Assignment expression Argument expression list assignment expression List references A postfix expression followed by an expression in square brackets is a postfix expression denoting a subscripted list reference The first of the two expressions must have type Listof T where T is some type and the other must have Number type Function Calls A function call is a postfix expression called the function designator followed by parentheses containing a possibly empty comma separated list of assignment expressions which constitute the arguments to the function In preparing for the call to a function a copy is made of each argument all argument passing is strictly by value A function may change the values of its parameter objects which are copies of the argument expressions but these changes cannot affect the values of the arguments Functions must be declared with explicit parameter types E 3 Unary Operators Unary Minus Operator 4 The operand of the unary minus operator must have type number or fraction The result is the negative of the operand Example Number called b b 4 b b Logical Negation Operator not The operand must be of type number The result is 1 if its operand is equal to 0 and 0 otherwise The result is of type number Example Number called b b 1 a not b a 0 Logical Magnitude Operator operand The operand must be of type string or list The result is the length of the string or the number of elements in the list The result is of type number Example Number called a string called b listof number called c b the cat a b a 7 c 5 3 a c a 5 Absolute Value Operator operand The operand must be of type number or fraction The result is the length of the string The result is of type number Example Number called a number called b a 8 b a b 8 5 E 4 Binary Arithmetic Operators Exponential Operator The exponential operator groups left to right The exponent must be of type number and positive The left operand may be a fraction or a number Exponential expression Exponential expression unary expression Unary expression Example Number called a number called b a 2 b 2 a b 4 Multiplicative Operators The multiplicative operators group left to right The operands for multiplication and division must be numbers or fractions The operands for remainder must be numbers If the second operand is zero for any of the above the result is 0 If one operand is a fraction the other is implicitly converted to a fraction Multiplicative expression Multiplicative expression Exponential expression Multiplicative expression Exponential expression Multiplicative expression Exponential expression Exponential expression Example Number number a 2 b a called a called b 4 3 a 2 2 b 0 Additive Operators The additive operators group left to right The operands for addition and subtraction must be numbers or fractions If one operand is a fraction the other is implicitly converted to a fraction 6 Additive expression Additive expression Multiplicative expression Additive expression Multiplicative expression Multiplicative expression Example Number called a a 2 4 3 a 3 E 5 String Operators Concatenation Operator The operator can be used to concatenate two strings It groups left to right string expression string expression string string expression string string expression string
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