La Mesa Language Reference Manual COMS 4115 Programming Languages and Translators Professor Stephen Edwards Michael Vitrano Matt Jesuele Charles Williamson Jared Pochtar 1 Introduction La Mesa is a language intended to make working with tables in a programmatic setting easier It is designed so that a programmer can use the full functionality of tables for retrieving storing and manipulating data without the additional hassle of working with SQL Relational databases form the core of many information technology systems that need to store large amounts of data in an efficient and organized manner While interacting with these databases with SQL is useful for efficiently accessing a particular subset of data there are many tasks that are either cumbersome or impossible For example applying a function to each record in a relational table is a multistep process requiring the programmer to write a query to retrieve the relevant data parse it apply the function and return the new data to the table Further there is no way to use SQL constructs to check input validity using regular expressions La Mesa attempts to simplify the interaction with relational databases by making tables firstclass objects Users are able to load information from a database manipulate it using the familiar imperative programming paradigm and optionally commit the data back to the database 2 Basic syntax La Mesa is intended to be a counterpart to Java i e it uses syntax derived heavily from Java and compiles into Java However it is distinct from Java so that a La Mesa program and a Java program are not confused To this end La Mesa borrows conventions from other imperative languages while keeping the flavor of imperative programming intact A La Mesa program is a series of tokens the type and nature of those tokens are described as follows There are five types of tokens comments keywords operators identifiers and literals Spaces newlines tabs and any other exotic nonprinting characters constitute whitespace they are necessary to separate tokens but are not recognized in any other way by the compiler 2 1 Comments The characters introduce a comment a newline terminates a comment There are no multi line comments 2 2 Keywords The following are keywords in La Mesa and are not to be used otherwise int null string float for if else while where table load func type import many one 2 3 Identifiers An identifier is anything beginning with a letter and continuing with any combination of letters numbers and underscores It can be used to describe variables tables or functions 2 4 Literals Any sequence of digits is an integer literal Any set of two sequences of digits separated by a decimal point is a floating point literal Any sequence of characters enclosed by double quotes is a string literal A list delimited by parentheses is a row literal eg Matt 654 W 123 St New York 3 Primitive Datatypes Internally values in La Mesa are treated as tables In other words while a user might type in the expression x 5 4 the La Mesa program treats the expression as the variable x describing a table is assigned to hold the table containing the singleton value 5 added to the table containing the singleton value 4 This is done to ensure that data will not be left in an indeterminate form during program execution it is also done to satisfy type constraint consistency All of this will be invisible to the programmer nevertheless certain operators acquire different powers and or necessitate different restrictions under this policy This is similar to the way that a database query engine such as MySQL would treat data Boolean Operators boolean equality test boolean greater than or equal to boolean less than or equal to boolean not equals boolean AND boolean OR boolean NOT La Mesa uses standard boolean operators that work on strings integers and floats and evaluates to either 0 false or something other than 0 true There is no special boolean data type Integer Floating Point Operations addition subtraction multiplication division exponentiation The La Mesa compiler defines all of the usual operators that work on both integer and floating point numbers One of the operands is restricted to be a singleton otherwise the compiler will throw an error String Operators string concatenation expression string interpolation The La Mesa compiler defines two operators on strings concatenation and interpolation For concatenation string1 string2 string1string2 La Mesa defines interpolation as in the code fragment string suffix 4115 string dept code COMS suffix In the above fragment the variable named dept code is assigned the string COMS4115 The value inside the curly braces must be a valid identifier or else it will cause an error Table Operators pipe operator The pipe operator is used to iterate over table rows La Mesa expects a valid table name to the left and an existing or new identifier for the row to the right of the operator For example the following statment iterates over the table Classes to find the row with id COMS4115 classes class if class class id COMS4115 matched class id push operator The push operator adds a new row to a table The new row must have the same width and column types as the table it is being added to otherwise a compiler error results return operator takes now left hand side adds the pushes the right hand side onto the table that will be returned Eg func many user explicitReturn many user in u in n copy u n name n name is cool ret n return ret becomes func many user implicitReturn many user in u in n copy u n name n name is cool n append operator The append operator adds a new column to a table The new column must have the same height as the table it is being added to otherwise a compiler error results table attribute datatype resolution operator Because La Mesa is strongly typed this operator is used to specify what type of data the program is to expect If the type resolved by the operator is not the type already in existence for the attribute then the compiler throws an error table column access operator This operator accesses a particular column within the table For example users name returns the name column of the users table A compiler error is produced if the user attempts to reference a column which is not in the table table row access operator This operator accesses a particular row within a table For example if the user wants to access the third row of a table the user would use the syntax if user user id 3 Matt user user id
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