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Max Version 1.30 - Reference Manual 1.0 Introduction Why should you bother to read about another programming language? After all there are hundreds of programming languages. Some are general purpose. Some are specialized for a particular field or application. You may have even found a favorite, perfect in every respect. If not, then here are some reasons for taking a closer look at Max: o No existing programming language has quite captured your approach to programming. o You are looking for a simple, block structured language with a good interpreter. o You want to be able to write powerful programs quickly and easily. o You don't think that a language needs to have a complicated syntax to be powerful. o You are looking for a language that can be extended and defined by the programmer. o You are tired of a language, or its creators, telling you how to program. o You are interested in programming languages for their own sake. o You want to design your own language and incorporate into it the best features of other languages. And there are dozens of other reasons to take a good look at Max. Remember, the source to the Max interpreter is available. If there is something you don't like, you can always change it. Now, back to the introduction... Max is a general purpose programming language that is based on C, LISP and the spirit of BASIC. It is not intended to replace any of those languages. Instead it is designed to make people think about programming languages and to consider how the design of the language affects the design and implementation of programs written in the language. Max was developed out of frustration with the syntactic inconsistencies and restrictions of modern programming languages. It provides the framework for a language and invites extension and customization using the basic syntactic element of the function, as well as the builtin preprocessor. Kernighan and Ritchie, in their guide to the C programming language, jokingly suggest that you use the C preprocessor to define BEGIN and END and use them instead of curly brackets. In Max you are encouraged to do this and anything else that will make you more comfortable with the language. Max is extensible. This means that new flow of control constructs can be defined and used just like the builtin ones. If you want to create an optimizing case statement, where the most frequently occuring cases are dynamically measured and tested first, you are free to do so. Max is not designed to shape programming style. It is designed to be shaped by it. An objective of Max is to promote programmer creativity and expressiveness through a minimum of restrictions. Max is not designed to perform fast Whetstones or long scientific calculations. And this version of Max does have some limitations, such as the lack of infix and postfix notation. Max is not a dead language. It is evolving. New features will be added in a way that is consistent with the framework of the language so that there will be a minimum of incompatibility. Most of all, Max is designed to be powerful, fun and easy to use. This overview of Max assumes that you have some familiarity with another programming language, such as C, LISP or BASIC. Max combines some of the useful features of each of these languages with its own unique characteristics. Consider the following Max program. It will give you a feeling for Max that will be helpful throughout the remainder of the reference manual. do { put ("What is your name? ") get (name) put ("Hello " name ", the time is " time ()) } do The symbols do, put, get and time are functions. The quoted words "What is your name? ", "Hello" and ", the time is " are literals. The symbols { and ( are argument list initiators. The symbols } and ) are argument list terminators. The use of parenthesis in put (...), get (...) and time (...) constitutes simple block closure. The use of curly brackets in do {...} do constitutes named block closure. The symbols and quoted words are collectively called tokens. 2.0 Tokens Tokens in Max can be broken down into six classes. These basic classes are functions, argument list initiators, argument list terminators, variables, literals and comments. The space, tab, comma and newline characters serve as delimiters and are otherwise ignored. Parentheses, square brackets, curly brackets and double quotes are also delimiters. 2.1 Functions Every statement in Max is a function. Functions are used for arithmetic, input and output, and flow-of-control. There is a large library of builtin functions and programs are written by defining new functions, called user defined functions. The language is completely extensible. Functions are passed values via an argument list and may return a result as a function value. Unlike the C programming language, arguments are not evaluated until they are referenced in the function. This allows user defined functions to implement flow-of-control constructs. The argument list to a flow-of-control function constitutes a block. The block may be delimited by three different sets of symbols to support different degress of block closure. 2.2 Argument List Initiators A function name is immediately followed by an argument list, which may be empty. The argument list is delimited on the left by an argument list initiator. The argument list initiator is used by Max to decide whether or not the preceding token is a function. There are three types of argument list initiators: left parenthesis, left square bracket and left curly bracket. See section 3.0 on Block Closure for information on the use of argument list initiators. 2.3 Argument List Terminators An argument list is delimited on the right by an argument list terminator. There are three types of argument list terminators: right parenthesis, right square bracket and right curly bracket. See section 3.0 on Block Closure for information on the use of argument list terminators. 2.4 Variables Values of any elemental type may be stored in a variable. This includes character strings, integers and floating point numbers. Aggregate types such as lists and arrays are referenced through an aggregate descriptor which may be stored in a variable. Variables are defined the first time that a value is stored in them. Until then, they return their name as their value, but runtime parameters may be selected that cause an error to be generated when an uninitialized variable is referenced. 2.5 Literals A sequence of zero or more characters surrounded by double quotes is considered a literal. All imbedded blanks are part of the literal. The double quotes that delimit the literal are not part of it. Non-printing characters may be included by using the backslash (\) escape convention. Valid escape sequences include: \\ - backslash \b - backspace \ - continuation (at end of line) \f - formfeed \n - newline \" - quote \r - return \t - tab An arbitrary ASCII code may be specified by using \0xnn where nn is the hexadecimal value of the ASCII code. Numbers are automatically classified as literals and do not need to be surrounded by double quotes. 2.6 Comments A semicolon introduces a comment in Max. The semicolon and anything else on the line are ignored. Semicolons in literals are not considered to be comment introducers. 3.0 Block Closure Max provides support for three different levels of block closure. See section 10 on the Preprocessor for a list of text replacement definitions that may be used to write clear block structured programs. 3.0.1 Simple Block Closure Simple block closure uses parentheses to delimit the argument list or block. They pair just as they do in conventional programming languages such as C. An if-then-else construct could be written as: if (boolean-expression then ( then-function-list ) else ( else-function-list ) ) A disadvantage to this type of closure is that it becomes difficult for the language processor (or programmer) to accurately identify the location of a missing parenthesis. 3.0.2 Named Block Closure To overcome this problem, Max provides "named block closure" which uses curly brackets to delimit the argument list. The right curly bracket is followed by the function name that precedes the corresponding left bracket. The above example can be rewritten as: if {boolean-expression then ( then-function-list ) else ( else-function-list ) } if In this example, the "if" block uses named block closure and the "then" and "else" blocks use simple block closure. The type of closure used is entirely up to the programmer. The Max language processor can detect block structure errors (i.e. missing parenthesis) within named blocks delimited by curly brackets. There is a tradeoff between the improved ability to detect errors using named block closure and the readability of simple block closure. 3.0.3 Multiple Block Closure Max also provides a shortcut to writing all of the right parenthesis or right curly brackets. It is called "multiple block closure" and is specified using square brackets: function-name [ function-list ] function-name A right square bracket, function name sequence pairs with the most recent function name, left square bracket sequence of the same name and closes all intervening blocks. An example of this is: if [boolean-expression then ( true-function-list ] if The "then" block is closed by the multiple block closure of the "if" block. Both simple and named blocks may be closed by right square brackets. 4.0 Data Types Max supports elemental and aggregate data types. 4.1 Elemental Elemental data types consist of strings and numbers and can be stored in a Max variable. 4.1.1 Strings A character string consists of a sequence of characters. Each character occupies one byte and any combination of eight bits is valid. There are numerous builtin functions that manipulate character strings. Character strings are automatically converted to numbers for use in numeric builtin functions. When converting character strings to numbers, the first non-numeric character terminates the conversion. If the character string is not a number then the result of the conversion is zero. 4.1.2 Numbers Max supports integer and real numbers and automatically converts between them when necessary. The maximum precision for integers is approximately 32 bits and the maximum precision for real numbers is 52 bits in the mantissa and 11 bits in the exponent. Max converts numbers to strings when necessary for string builtin functions. 4.2 Aggregate Data Max supports arrays and lists. They are known as aggregate data types and are referenced using an aggregate descriptor. The aggregate descriptor is returned by the builtin function that allocates the data structure and is then used for all other builtin functions that manipulate the data. Aggregate descriptors are small integers and may be stored in element variables. Arrays and lists can be mapped together so that the data can be referenced using either array or list functions. 4.2.1 Arrays Arrays are explicitly allocated and freed, and are accessed by an array descriptor. The size of the array as well as optional initializers is specified on allocation. There are two types of arrays. Indexed arrays are similar to arrays in other programming languages. The elements of an indexed array are referenced by an integer index. The other type of array is a keyed array. Elements of a keyed array are referenced by a character string key. Keyed arrays form a simple associative memory. 4.2.2 Lists Lists are explicitly allocated and freed and are accessed by a list descriptor. Elements may be pushed and popped on the head or tail of the list, at the current location, or on a sub node. The current location may be set to the head or tail and updated by moving it to the previous, next or sub node. Lists with sub nodes form binary trees. Lists may be sorted, optionally by a user supplied compare function. 4.3 Patterns A large library of pattern matching functions allows text to be searched for patterns. Matches can be assigned to variables for subsequent processing. Patterns are explicitly allocated and freed and are accessed by a pattern descriptor. 5.0 Storage Types Elemental data (variables) may be allocated automatic or static storage. Aggregates are explicitly allocated static storage. Aggregates must be explicitly freed when they are no longer needed. 5.1 Automatic Unless otherwise defined, all variables in user defined functions are automatic. They are allocated storage from a stack when the function is entered and the storage is freed when the function returns. Storage may also be explicitly allocated using the auto builtin function. Storage allocated via auto may be explicitly freed. It is automatically freed when the function returns. 5.2 Static Static storage may be used when a variable must retain its contents between calls to a function. It must be explicitly allocated using the "static" builtin function. Static storage must be explicitly freed when it is no longer needed. 5.3 Shared Two builtin functions, export and import, may be used to share access to automatic and static storage between user defined functions. These functions specify the name of the variable and optionally the name of the function to export to or import from. 5.4 Transient Functions are stored in an area of memory called the transient area. General purpose functions can be locked in the transient area using the tset builtin function. Transient functions can be cleared from memory using the tclear builtin function. The transient area itself can be subdivided into frames using the tpush and tpop builtin functions. Each frame can have a locked area and a transient area. 6.0 Identifiers Function and variable names are known collectively as identifiers. There are no reserved keywords, although parameters may be set that prevent redefinition of builtin function names as user defined functions. 6.1 Naming Rules Names may not begin with a digit, a minus sign or a decimal point. They may not contain spaces, tabs, commas, newlines, parentheses, square brackets, curly brackets or semicolons. 6.2 Scope There are two types of user defined functions: external and internal. External functions may be called from other external functions and can be invoked as commands. Internal user defined functions are only visible within the function that defines them. Variables in user defined functions are only visible within the function that defines them and any internal functions. Variables defined in internal user defined functions are not visible in the containing function. 7.0 Recursion All external user defined functions in Max may be invoked recursively. Internal user defined functions do not support recursion. 8.0 Error and Control-C Handling Errors may be trapped and handled by user defined functions. A system error level may also be set. Errors with a severity greater than the error level cause a message to be printed. The severity of errors is divided into three classes: warning, error and fatal. Control-C may also be trapped and handled by a user defined function. The default action is to terminate the currently executing function and print the step number that was interrupted. 8.1 Warnings Warnings are severity level 0. An error message is printed and the function returns -1 to indicate an error occured. The containing user defined function, if any, may check the return code and is free to continue executing. 8.2 Errors Errors are severity level 1. An error message is printed and the function returns -1 to indicate an error occured. The containing user defined function, if any, is terminated. 8.3 Fatal Fatals are severity level 2. An error message is printed and the interpreter is terminated. This type of error cannot be caught by an error handler. 9.0 Debugging Max provides support for step tracing, single step execution, stack history display and stack relative variable contents display. Only step tracing is available during pattern matching. Any Max command may be entered after step completion during single step execution. 10.0 Preprocessor Max uses a source preprocessor that supports text replacement and include files. The preprocessor may be disabled. It may also be used in an optimized mode where only tokens that begin with characters in a specific range, such as A to Z (capitalized), are checked for replacement. 10.1 Text Replacement A preprocessor text replacement statement takes the form: $replace ("old" "new") where any subsequent occurence of "old" is replaced by "new". Please note that both the "old" and "new" text should be enclosed in quotes. The text replacement feature may be used to define structured flow-of-control names to make Max programs more readable. The following definitions are useful in writing block structured programs: $replace ("Function" "define [") $replace ("EndFunction" "] define") $replace ("Begin" "(") $replace ("End" ")") $replace ("While" "while {") $replace ("EndWhile" "} while") $replace ("Until" "until {") $replace ("EndUntil" "} until") $replace ("For" "for {") $replace ("EndFor" "} for") $replace ("Loop" "loop {") $replace ("EndLoop" "} loop") $replace ("If" "if [") $replace ("EndIf" "] if") $replace ("Then" "then {") $replace ("EndThen" "} then") $replace ("Else" "else {") $replace ("EndElse" "} else") $replace ("Case" "case {") $replace ("EndCase" "} case") $replace ("Select" "select {") $replace ("EndSelect" "} select") $replace ("When" "when {") $replace ("EndWhen" "} when") $replace ("Default" "default {") $replace ("EndDefault" "} default") $replace ("Do" "do {") $replace ("EndDo" "} do") These preprocessor replacement specifications may be found in the file named block.max in the standard distribution. 10.2 Replacement Redefinition A symbol may be redefined by subsequent preprocessor replace statements. Each one hides the definition of the previous one. The previous definition may be restored by using the nreplace directive. The syntax for nreplace is: $nreplace ("Name") where "Name" is the name of a symbol from a previous replace statement. The most recent definition of "Name" is removed and any previous definition is visible. 10.3 Text Inclusion The include preprocessor directive may be used to add text from other files to a source file. It is used as follows: $include ("pathname") Where "pathname" is the name of the file that you want to include. 11.0 Configuration The maximum length of function names, variable names, and quoted literals may be set as a runtime parameter. The default is 128 bytes. The maximum amount of storage allocated for variables as well as the maximum size of many other internal data structures may be specified by runtime parameters. 11.1 Startup File When started, Max searches the directories in the PATH environment variable for a file called config.max. This file may contain values that override defaults for the amount of storage allocated to internal data structures. Each line in the file is in the same format as a command line parameter. The file may also contain the name of Max source files to evaluate during initialization. This allows Max to load libraries of user defined functions. 11.2 Command Line Command line parameters may be specified to override values in the configuration file. 12.0 Execution Environment A choice of integrated or interactive execution environments is available with Max. 12.1 Integrated A multiwindow integrated environment called MaxEdit is available. This allows program development to occur in one window while program execution and output is monitored in another window (though not multitasked under DOS). Any number of tiled (adjacent) or piled (overlapping) windows may be created. 12.2 Interactive If the integrated environment is not used, Max enters an interactive mode where lines are read from the keyboard until a latest replacement definition may be removed and the previous complete command function reference is entered, whereupon evaluation of the function begins and output is displayed on the console.