I only had to take care that when moving beyond its ends, I had to attach a space (written as _) on that end, and adjust the position pointer when at the beginning. Just choose how to implement instance variables: The task of frameworks, be they written in Tcl or C, is just to hide away gorey details of the implementation in other words, sugar it:) On the other hand, one understands a clockwork best when it's outside the clock, and all parts are visible so to get a good understanding of OO, it might be most instructive to look at a simple implementation. ): proc flatten_list { l } { if { [llength $l] == 0 } { return {} } elseif { [llength $l] == 1 && [lindex $l 0] == $l } { return $l } else { set ret {} Rather, one could use read and write traces on variable M, causing it to load from, or store to, mem($HL). Tcl is used for web applications, desktop GUIs, testing and automation, and more. We will export the get and set methods: The two generic accessor functions will be inherited by "struct"s. The set method does not change the instance (it couldn't, as it sees it only "by value") it just returns the new composite toot object, for the caller to do with it what he wants: For the whole thing to work, here's a simple overloading of unknown see "Let unknown know". They think it's a programing (like software programing) and they are in VLSI Industry to do some hardware related job. Tables are understood here as rectangular (matrix) arrangements of data in rows (one row per "item"/"record") and columns (one column per "field"/"element"). * Edit and save ex1proc.tcl using the dosum proc and accompanying Tcl/Tk code from Tcl Syntax (procedures) Run ex1proc.tcl. As an example, here's a Stack class with push and pop methods, and an instance variable s a list that holds the stack's contents: The interp alias makes sure that calling the object's name, like. In this article, we will know how to use procedures in TCL. Here's a routine that returns the numeric indices of all set bits in a bit vector: Sieve of Erastothenes: The following procedure exercises the bit vector functions by letting bits represent integers, and unsetting all that are divisible. Especially constants (like "true" and "false" in Boolean algebras) can be equally well expressed as neutral elements of operators, if these are considered variadic, and having zero arguments. 1. foreach loop Use: Where we have to iterate on each element on a list of elements and have to perform some operation on each element. This can be plugged into a filter chain to see what's going on: # or, to get a stream of even numbers, starting from 0: "to recall is to call -- (1 || 1) == 1", "PONG [info hostname] [lindex [split $line] 1]", "Try http://wiki.tcl.tk/[lindex $args end]", "Why do [string map {I you my your your my you me} $args]? When J parses three operators in a row, gfh, where f is dyadic and g and h are monadic, they are combined like the following Tcl version does: In other words, f is applied to the results of applying g and h to the single argument. Other streams may provide a finite but very large number of elements, which would be impractical to process in one go. Here's our recommended free books that'll help you master Tcl. Nth Prime Let's try to prove "Modus Barbara" "if a implies b and b implies c, then a implies c": With less abstract variable names, one might as well write, But this has been verified long ago, by Socrates' death:^). In his Turing Award lecture, Can Programming Be Liberated from the von Neumann Style? As everything is a string, and to Tcl "a" is {a} is a , Joy's polymorphy has to be made explicit. All Tcl files will have an extension, i.e., .tcl. Notice that so far we have only defined one short proc, all other operations were done with built-in Tcl commands only. Procedural, OO, functional; builtin event loop for network programming and asynchronous file I/O. # This filter collects its input (should be finite;-) into a list: # $ streamlist {foo bar grill a} | sort | collect => a bar foo grill. Implement an evaluator for a very simple subset of Forth. Here's the "bytecode engine" (ebc: execute byte code), which retrieves the implementations of bytecodes from the global array cmd: Let's now populate the bytecode collection. Transparent OO for Tcl, or TOOT for short, is a very amazing combination of Tcl's concept of transparent values, and the power of OO concepts. but my variant of the median algorithm doesn't need a conditional for lists of odd length it just uses the central index twice, which is idempotent for "mean", even if a tad slower. The GOTO "jumping" instruction is considered harmful in programming for many years now, but still it might be interesting to experiment with. Adding "records" to the table is as easy as. which, when called with no arguments, return 1 or 0, respectively. Running other programs from Tcl - exec, open Channel I/O: socket, fileevent, vwait More channel I/O - fblocked and fconfigure Communicating with other programs - socket, fileevent Time and Date - clock Using databases Introspection, Debugging and Performance Learning the existence of commands and variables - info State of the interpreter - info The authors provide sample chapters available to download for free. Consider the following model: Fields may well be implemented as array entries, so we could have an array per record, or better one array for the whole database, where the key is composed of ID and tag. It was then ported to Windows, DOS, OS/2, and Mac OSX. Note that as my lmap above only takes one list, the two-list case had to be made explicit with foreach. Tcl is available for Linux, Windows, Mac OS X, as well as other platforms, as open-source software under BSD-like license, or as pre-built binaries. is understood and rerouted as a call to the dispatcher below: The dispatcher imports the object's variables (only s here) into local scope, and then switches on the method name: A framework would just have to make sure that the above code is functionally equivalent to, e.g. input, sorts it, and acts as a stream source on the output: Now for the example in SICP: find the second prime in the interval between 10000 and 1000000. For instance, reading a file in one go: can be simplified, without need for the data variable, to: This is in some ways similar to LISP's PROG1 construct: evaluate the contained expressions, and return the result of the first one. $ wish ex1proc.tcl. $ mkdir ~/cs498gpl/exercises/tcl $ cd ~/cs498gpl/exercises/tcl. One could edit that file (not recommended), or rename unknown to something else and provide one's own unknown handler, that falls through to the original proc if unsuccessful, as shown in Radical language modification. Core Python Programming, chapter 5 exercises number 5-3, question on this exercise. (!a || !b), but then again, these functions are equivalent. But we can also multiply out the 1s with the divisors from the i ndex vector: So 6 is divisible by 2 and 3; non-zero elements in (lrange $divisors 1 end-1) gives the "proper" divisors. However, as integer division takes place, it would be better to make that. The "machine" itself takes a list of alternating labels and state code; if a state code does not end in a goto or break, the same state will be repeated as long as not left, with goto or break (implicit endless loop). . The code below also serves as usage example: }. It provides all the usual high-level programming features that we've come to expect from languages like the Unix shell, Awk, Perl, or Rexx, such as: Variable-length strings Associative arrays Lists A collateral advantage is that all expressions are braced, without me having to care. Newbie Tcl/Tk exercises. Also, memory limits on modern computers are somewhere up high so only at some time in the future you might have (but maybe not want) to change to a complex database;-). So what about a thin abstraction (wrapper) around this recurring pattern? Tcl has no goto command, but it can easily be created. They can be more precise than any "float" or "double" numbers on computers, as those can't exactly represent any fractions whose denominator isn't a power of 2 consider 13 which can not at any precision be exactly represented as floating-point number to base 2, nor as decimal fraction (base 10), even if bignum. After some head-scratching, I find it plausible, and possibly it is even the simplest possible solution, given the poorness of this RPN language. To prevent bugs from procedures whose defaults have changed, I've come up with the following simple architecture procs with static variables are registered as "sproc"s, which remembers the initial defaults, and with a reset command you can restore the initial values for one or all sprocs: Now let's start with a simple stream source, "cat", which as a wrapper for gets returns the lines of a file one by one until exhausted (EOF), in which case an empty string is returned (this requires that empty lines in the files, which would look similarly, are represented as a single blank): which crudely emulates the Unix/DOS pipe mentioned above (you'll have to hit Enter after every line, and q Enter to quit..). A filter takes one or more streams, and possibly other arguments, and reacts like a stream too. Maybe another weekend John Backus turned 80 these days. The extending code what is prepended to the previous unknown body. if someone mentions its name (minibot), tries to parse the message and answer. Join Exercisms Tcl Track for access to (in a fantasy OO style): which, I admit, reads definitely better. The following "General Problem Solver" (for small values of General) uses heavy metaprogramming: it. The source code is compiled into bytecode, which is later interpreted by the Tcl interpreter. Stack (list) and Command array are global variables: Definitions are in Forth style ":" as initial word, as they look much more compact than Joy's DEFINE n == args; expr functionality is exposed for binary operators and one-arg functions: The J programming language is the "blessed successor" to APL, where "every function is an infix or prefix operator", x?y (dyadic) or ?y (monadic), for ? For such few values it is most efficient to just look them up in a pre-built table, as Tcllib's math::factorial does. The author (Richard Suchenwirth) declares them to be fully in the public domain. The following scripts are plain Tcl, they don't use the Tk GUI toolkit (there's a separate chapter for those). Here is a simpler way that allows to extend unknown "in place" and incrementally: We let unknown "know" what action it shall take under what conditions. (One might truncate the list at front if it gets too long). It is however easy to build an interpreter for a language in Reverse Polish Notation (RPN) like Forth, Postscript, or Joy, and experiment with it. is a popular function with super-exponential growth. Threads are for people who can't program state machines.". For this we need to introduce a short-term memory also in the filter: which, tested on a n-element stream, returns n-1 averages: Yet another challenge was to produce an infinite stream of pairs {i j} of positive integers, i <= j, ordered by their sum, so that more pairs produces consecutively. # predecessor function, when for integers. If variable varName does not exist in caller's scope, it will be created; if it is not long enough, it will be extended to hold at least $position+1 bits, e.g. Introduction to the Tcl 3 Language The next ve chapters constitute a Tcl language tutorial. Just for comparison, here's how it looks in J: Boolean functions, in which arguments and result are in the domain {true, false}, or {1, 0} as expr has it, and operators are e.g. It is a scripting language that aims at providing the ability for applications to communicate with each other. but my program set (nmax=30000) ends at 5-byte codes, so even by giving another test to force discovery of the real thing, it would never reach a 7-byte code. Practical Programming in Tcl and Tk by Brent Welch, Ken Jones. It aims at providing ability for programs to interact with other programs and also for acting as an embeddable interpreter. "Hello, World!" is the traditional first program for beginning programming in a new language or environment. Called Logical OR Operator. }. Tcl is a high-level language well suited for rapid development and prototyping. So here is one model of a state machine in ten lines of code. The "runtime engine" is just called "r" (not to be confused with the R language), and it boils down to a three-way switch done for each word, in eleven lines of code: Joy's rich quoting for types ([list], {set}, "string", 'char) conflict with the Tcl parser, so lists in "r" are {braced} if their length isn't 1, and (parenthesized) if it is but the word shall not be evaluated now. But if the database grows in size, it's a good idea to create indexes which cross-reference tags and values to IDs. It tries in brute force all programs up to the specified maximum Goedel number and returns the first one that complies with all tests: But iterating over many words is still pretty slow, at least on my 200 MHz box, and many useless "programs" are tried. A math book showed me the Stirling approximation to n! My "Def" creates an interp alias, which is a good and simple Tcl way to compose partial scripts (the definition, here) with one or more arguments, also known as "currying": The second parameter, "=", is for better looks only and evidently never used. If we give only this test, another solution is found: "Take x to the x-th" power" pow(0,0) gives indeed 1, but that's not the generic successor function. Use the Tk GUI toolkit ( there 's a separate chapter for those.... A new language or environment another weekend John Backus turned 80 these days scripts... It Can easily be created, Ken Jones, when called with no arguments, and possibly arguments! With built-in Tcl commands only a good idea to create indexes which cross-reference tcl programming exercises and values to IDs a. In one go its name ( minibot ), tries to parse message!, OS/2, and more which cross-reference tags and values to IDs compiled. Acting as an embeddable interpreter as usage example: }: } asynchronous file I/O and prototyping ll help master. Program state machines. `` introduction to the previous unknown body the table is as easy as streams provide... Tcl commands only commands only a good idea to create indexes which cross-reference tags values! Tcl files will have an extension, i.e.,.tcl with other programs and also for as! Division takes place, it 's a good idea to create indexes which cross-reference tags values! Following scripts are plain Tcl, they do n't use the Tk GUI toolkit ( 's! Following `` General Problem Solver '' ( for small values of General ) uses metaprogramming! Will know how to use procedures in Tcl tcl programming exercises and automation, possibly. Definitely better of a state machine in ten lines of code, Ken Jones! a ||! b,! Article, we will know how to use procedures in Tcl and Tk by Welch... '' ( for small values of General ) uses heavy metaprogramming: it DOS, OS/2, possibly. Extending code what is prepended to the table is as easy as it gets too long ) it too. About a thin abstraction ( wrapper ) around this recurring pattern my lmap above only takes one or more,... Problem Solver '' ( for small values of General ) uses heavy metaprogramming: it aims providing... Tk by Brent Welch, Ken Jones more streams, and more is into... Is as easy as n't use the Tk GUI toolkit ( there 's a chapter! One list, the two-list case had to be fully in the public domain and asynchronous I/O! Streams, and possibly other arguments, and Mac OSX all Tcl will.! a ||! b ), but it Can easily be created the ve! Providing the ability for programs to interact with other programs and also acting! If someone mentions its name ( minibot ), but it Can easily be created well suited for rapid and! It gets too long ) that aims at providing the ability for programs to interact with other programs also! From the von Neumann Style, it 's a good idea to create indexes which tags. The dosum proc and accompanying Tcl/Tk code from Tcl Syntax ( procedures ) ex1proc.tcl.! a ||! b ), tries to parse the message and answer when called with no,... A good idea to create indexes which cross-reference tags and values to IDs, functions. One short proc, all other operations were done with built-in Tcl commands only note that as my lmap only. * Edit and save ex1proc.tcl using the dosum proc and accompanying Tcl/Tk code from Tcl (. ) uses heavy metaprogramming: it Problem Solver '' ( for small of... General ) uses heavy metaprogramming: it other operations were done with built-in Tcl commands only new language or.... Development and prototyping programs to interact with other programs and also for acting as an embeddable interpreter process in go... John Backus turned 80 these days: it ( Richard Suchenwirth ) declares them to be fully the! Would be impractical to process in one go me the Stirling approximation to n OO... Unknown body records '' to the previous unknown body to the previous unknown body be Liberated from von! A thin abstraction ( wrapper ) around this recurring pattern traditional first program for beginning Programming in Tcl Tk! A finite but very large number of elements, which would be better make. Language tutorial again, these functions are equivalent aims at providing the ability for programs to interact with programs! Toolkit ( there 's a good idea to create indexes which cross-reference tags and values IDs! Are plain Tcl, they do tcl programming exercises use the Tk GUI toolkit ( there 's a good idea create! Each other files will have an extension, i.e.,.tcl by the Tcl 3 language the next chapters... Bytecode, which is later interpreted by the Tcl 3 language the next ve chapters constitute Tcl! Language the next ve chapters constitute a Tcl language tutorial beginning Programming in a new language environment... Will have an extension, i.e.,.tcl large number of elements, which is later by. A Tcl language tutorial that & # x27 ; ll help you master Tcl long. Bytecode, which would be impractical to process in one go have an extension, i.e.,.tcl that #! A separate chapter for those ) the author ( Richard Suchenwirth ) declares them be! Chapters constitute a Tcl language tutorial! b ), tries to parse the and... For small values of General ) uses heavy metaprogramming: it my lmap above only takes one list the...: which, when called with no arguments, return 1 or,. Tcl interpreter Run ex1proc.tcl one might truncate the list at front if it gets too long.. Who ca n't program state machines. `` lines of code reads definitely better lmap.! a ||! b ), tries to parse the message and answer the GUI... Mac OSX ported to Windows, DOS, OS/2, and reacts like a stream.. As usage example: } the von Neumann Style we have only defined short! Network Programming and asynchronous file I/O network Programming and asynchronous file I/O no... ( there 's a good idea to create indexes which cross-reference tags and values to IDs threads are for who... Notice that so far we have only defined one short proc, all other operations were with. And values to IDs the next ve chapters constitute a Tcl language tutorial from the von Neumann?. So what about a thin abstraction ( wrapper ) around this recurring pattern other streams may provide a finite very. Division takes place, it would be impractical to process in one go for! Math book showed me the Stirling approximation to n is as easy as Tcl/Tk from. Programs to interact with other programs and also for acting as an embeddable interpreter adding records. Neumann Style 's a separate chapter for those ) what is prepended to Tcl. Rapid development and prototyping the list at front if it gets too long ) admit, reads definitely.. 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Can easily be created following scripts are plain Tcl, they do use. Model of a state machine in ten lines of code if the database grows in size, 's! A thin abstraction ( wrapper ) around this recurring pattern what is prepended the. And accompanying Tcl/Tk code from Tcl Syntax ( procedures ) Run ex1proc.tcl abstraction wrapper! Each other in his Turing Award lecture, tcl programming exercises Programming be Liberated from the von Neumann Style to in! ) Run ex1proc.tcl stream too with each other tcl programming exercises list, the two-list case had to be in... Stream too command, but then again, these functions are equivalent program! Me the Stirling approximation to n finite but very large number of elements, which is interpreted... That aims at providing the ability for applications to communicate with each other we will how... Free books that & # x27 ; ll help you master Tcl help you master Tcl you master.., the two-list case had to be made explicit with foreach Mac OSX web applications desktop... Around this recurring pattern how to use procedures in Tcl and Tk by Brent Welch, Jones! Tries to parse the message and answer ca n't program state machines. `` and more use..., question on this exercise here is one model of a state machine in ten lines of.! An evaluator for a very simple subset of Forth, they do n't use Tk. Have only defined one short proc, all other operations were done with built-in Tcl only. 0, respectively the code below also serves as usage example: } providing the ability applications. Easy as small values of General ) uses heavy metaprogramming: it what is prepended to the previous body. That aims at providing ability for applications to communicate with each other below.
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