returns the first solution found, or else an empty string: A record is a nonempty set of fields with a unique ID, A field is a pair of tag and nonempty value, both being strings, a set F of functions that map objects into objects (, an operation, application (very roughly, eval), a set FF of functional forms, used to combine functions or objects to form new functions in F, a set D of definitions that map names to functions in F, "tcl" evaluates the top of stack as a Tcl script, scalar @ scalar scalar (like expr does), vector @ vector vector (all of same dimensions, element-wise), measure the stack balance for each bytecode, iterate once over very many possible programs, computing their stack balance, partition them (put into distinct subsets) by stack balance, perform each 'discovery' call only on programs of matching stack balance, Brute force is simple, but may demand very much patience (or faster hardware), The sky, not the skull is the limit what all we can do with Tcl:), classes can be defined, with variables and methods, objects are created as instances of a class, objects are called with messages to perform a method, or just as parts of a transparent value, with TOOT, a is the state in which they can be applied, b is the character that must be read from tape if this rule is to apply, D is the direction to move the tape after writing (R(ight) or L(eft)), e is the state to transition to after the rule was applied, Every animal is suitable for a pet, that loves to gaze at the moon, No animals are carnivorous, unless they prowl at night, No animals ever take to me, except what are in this house, Animals that prowl at night always love to gaze at the moon. Elements are not removed by the popping, but (if necessary) when re-pushing. Tcl 8.5 has the {*} construct to undo one-level of list packing (discussed on the Confluence page). Tests are done with this minimal "framework": The dot product of two vectors is a scalar. 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. Every language has its own way of doing things. 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. Tcl supports multiple programming paradigms, including object-oriented . 13Solving cryptarithms 14Database experiments 14.1A simple array-based database 14.2Tables as lists of lists 15Programming Languages Laboratory 15.1GOTO: a little state machine 15.2Playing Assembler 15.3Functional programming (Backus 1977) 15.4Reusable functional components 15.5Modelling an RPN language 15.6Tacit programming 16Vector arithmetics But the admittedly still very trivial challenge was met in truly function-level style, concerning the definitions of median, center and mean no variable left behind. "Tacit programming" (tacit: implied; indicated by necessary connotation though not expressed directly) is one of the styles possible in J, and means coding by combining functions, without reference to argument names. Of course, there are some who say: "Advocating object-orientated programming is like advocating pants-oriented clothing: it covers your behind, but often doesn't fit best" Quite a bunch of what is called OO can be done in pure Tcl without a "framework", only that the code might look clumsy and distracting. The best part, its 100% free for everyone. All of Boole's algebra can be expressed in this calculus: We can test it with the classic "ex contradictione quodlibet" (ECQ) example "if p and not p, then q" for any q: So formally, q is true, whatever it is:) If this sounds overly theoretic, here's a tricky practical example in puzzle solving, Lewis Carroll's last sorites (pp. For a real 8080, one would have to say. Newbie Tcl/Tk exercises. line-ends \r\n are not standardized to \n as usual in C), and prints as many lines as needed which each contain 16 bytes in hexadecimal notation, plus, where possible, the ASCII character. Implement an evaluator for a very simple subset of Forth. But func isn't limited to math functions (which, especially when recursive, come out nice), but for expr uses in testing predicates as well: Exposing expr binary arithmetic operators as Tcl commands goes quite easy too: For "-", we distinguish unary and binary form: Having the modulo operator exposed, gcd now looks nicer: For unary not I prefer that name to "! In Tcl, a sensible implementation for compact data storage would be as a list of lists. See the examples soon to come. of your code and Here I use a global array for recording results: delivers in hardly noticeable time the R. numbers 1729, 4104, 13832 Or, how's this infinite Fibonacchi number generator, which on more fibo produces all the F.numbers (0,1,1,2,3,5,8,13,21) you might want? Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. Tcl's lsort is stable, so items with equal priority will remain in the order in which they were queued: A practical application is e.g. Of course I can't use circumfix brackets as operator name, so let's call it constr: which returns correctly 3. Implication (if a then b, a -> b) can in expr be expressed as $a <= $b just note that the "arrow" seems to point the wrong way. For such few values it is most efficient to just look them up in a pre-built table, as Tcllib's math::factorial does. This works fine on some well-known cryptarithms: There are lots of complex databases around. question: In this weekend fun project to emulate machine language, I picked those parts of Intel 8080A/8085 Assembler (because I had a detailed reference handy) that are easily implemented and still somehow educational (or nostalgic;-). When two operands occur together, the "hook" pattern is implied, which might in Tcl be written as: As KBK pointed out in the Tcl chatroom, the "hook" pattern corresponds to Schnfinkel/Curry's S combinator (see Hot Curry and Combinator Engine), while "fork" is called S' there. Learn and practice Tcl by completing 122 exercises that explore different concepts and ideas. Syntax: foreach var $Var_list { //operations for each $var } Example: and Insert is better known as fold, I suppose. Another example, cooked up by myself this time, computes the average of a list. was instigated by the fact that in J, "NB." Tcl is a scripting language somewhat like Perl but extensible and clearer. This is provided e.g. Luckily we have an if in Tcl (and it certainly fares better in byte-code compilation), but on leisurely evenings it's not the microseconds that count (for me at least) it's rather reading on the most surprising (or fundamental) ideas, and demonstrating how easily Tcl can bring them to life Never afraid of anything (as long as everything is a string), a discussion in the Tcl chatroom brought me to try the following: let the computer write ("discover") its own software, only given specifications of input and output. Grade School Given students' names along with the grade that they are in, create a roster for the school. 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. A collateral advantage is that all expressions are braced, without me having to care. For instance, we want all books printed before 1980: We might also store our patrons in the same database (here in a different style): Without a concept of "tables", we can now introduce structures like in relational databases. Implementation is as a "little-endian" list of integers, where bits 0..31 are in the first list element, 32..63 in the second, etc. I first don't understand why all premises can be just written in a row, which amounts to implicit "or", but it seems to work out well. 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 For instance, here's how to make an authors' index in four lines: gives us a books list of all authors matching the given glob pattern (we reuse Tcl's functionality, instead of reinventing it). Before we start, a word of warning: maintaining state of a procedure is done with default arguments that may be rewritten. To find out how big a paper format is, one can measure an instance with a ruler, or look up appropriate documentation. Tcl doesn't have this mechanism built-in (and it would be hard to do it exactly the same way, because everything is a string), but a similar mechanism can easily be adopted, and it doesn't look bad in comparison: If the docstring is written in comments at the top of a proc body, it is easy to parse it out. This silly example demonstrates member access and some string manipulation: At university, I never learned much about Turing machines. Conversely, postulating non-equivalence turns out to be false in all cases, hence a contradiction: So again, we have a little proving engine, and simpler than last time. In this article, we will know how to use procedures in TCL. Sorting roman numerals: I,V,X already come in the right order; for the others we have to introduce temporary collation transformations, which we'll undo right after sorting: As "control structures" are really nothing special in Tcl, just a set of commands, it is easier than in most other languages to create one's own. fractions, can be thought of as pairs of integers {numerator denominator}, such that their "real" numerical value is numerator/denominator (and not in integer nor "double" division!). Join Exercisms Tcl Track for access to I added converters between characters and integers, and between strings and lists (see the dictionary below). Threads are for people who can't program state machines.". Create this and all subsequent Tcl exercise programs under your exercises/tcl subdirectory. and returns the result of calling that form: Now to use it (I admit the code is no easy reading): Testing: we define a "struct" named foo, with two obvious members: Modify part of the foo, and assign it to another variale: Struct-specific methods can be just procs in the right namespace. 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. Factorial (n!) This may be used for Boolean properties of numerically indexed sets of items. Introduction to the Tcl 3 Language The next ve chapters constitute a Tcl language tutorial. Book . # Multiple documentation lines are allowed. More experiments to discover the hypot() function: Hm the 3 is duplicated, divided by itself (=1), which is added to 4. Enrol for e-learning course for self paced learning. A math book showed me the Stirling approximation to n! Tcl (pronounced "tickle" or as an initialism) is a high-level, general-purpose, interpreted, dynamic programming language.It was designed with the goal of being very simple but powerful. In a frequent parlage, priority 1 is the "highest", and the number increases for "lower" priorities but you could push in an item with 0 for "ultrahigh";-) Popping a stack can be done like this: Popping a queue is similarly structured, but with so different details that I found no convenient way to factor out things: Popping a priority queue requires sorting out which item has highest priority. 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. Tcl is a string based scripting language. ", as it might also stand for factorial and see the shortest function body I ever wrote:^): Without big mention, functions implemented by recursion have a pattern for which func is well suited (see fac and gcd above). If a field content contains spaces, it must be quoted or braced too: Sorting a table can be done with lsort -index, taking care that the header line stays on top: Removing a row (or contiguous sequence of rows) by numeric index is a job for lreplace: Simple printing of such a table, a row per line, is easy with. The partitioning helps very much in reducing the number of candidates. In his Turing Award lecture, Can Programming Be Liberated from the von Neumann Style? Its combination of text processing, file manipulation and system control features make it ideal for this purpose. Once you've solved an exercise, submit it to our volunteer team, and they'll give you hints, ideas, and feedback on how to make it feel more like what you'd normally see in Tcl - they'll help you discover the things you don't know that you don't know. Write a function to determine if a list is a sublist of another list. The print version is available from Amazon in USA/Canada and their European sites including UK , Germany , France , Spain and Italy . We have Boolean operators in expr, so here goes: The only unary operator NOT can be written in terms of nand: .. and everything else can be built from them too: Here's some testing tools to see whether an implementation is correct, look at its truth table, here done as the four results for A,B combinations 0,0 0,1 1,0 1,1 side note: observe how easily functions can be passed in as arguments: To see how efficient the implementation is (in terms of NAND units used), try this, which relies on the fact that Boolean functions contain no lowercase letters apart from the operator names: As a very different idea, having nothing to do with NAND as elementary function, the following generic code "implements" Boolean functions very intuitively, by just giving their truth table for look-up at runtime: Cryptarithms are puzzles where digits are represented by letters, and the task is to find out which. It may be interesting to note that this language has truly minimal syntax the only rule is: each script ("word") composed of any number of bytecodes is well-formed. If you are able to automate below few task, more then 50% of work (based on TCL) can be done easily. 71 coding exercises for C on Exercism. For Beginners) Tcl and Tk Programming for the Absolute Beginner Windows 10 Troubleshooting: Windows 10 Manuals, Display Problems, Sound Problems, Drivers and Software . So to create such a table with a defined field structure, but no contents yet, one just assigns the header list: Note the double bracing, which makes sure tbl is a 1-element list. Procedural, OO, functional; builtin event loop for network programming and asynchronous file I/O. Try to swap the inputs: Another dirty trick: get square root of 4, add to 3 presto, 5. This makes sense, even in Tcl, where one might implement them as. (One might truncate the list at front if it gets too long). The Tcl track on Exercism has 122 exercises to help you write better code. But bare-bones has its advantages too: in order to see how a clockwork works, you'd better have all parts visible:). personal mentoring, So I tried with another a^2+b^2=c^2 set, and HEUREKA! To try this in Tcl, here's a truth table generator that I borrowed from a little proving engine, but without the lsort used there the order of cases delivered makes best sense when the first bit is least significant: }. There are over 200 exercises with solutions that run on both Unix and Windows platforms. For functional composition, where, say for two functions f and g. again a proc is created that does the bracket nesting: Why Backus used Transpose on the input, wasn't first clear to me, but as he (like we Tclers) represents a matrix as a list of rows, which are again lists (also known as vectors), it later made much sense to me. His two axioms are: and these can be implemented by a string map that is repeated as long as it makes any difference (sort of a trampoline) to simplify any expression consisting only of operators and constants (which are operators with zero arguments): which maps <><> to <>, <<>> to "", and returns <> for "true". 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. here is an implementation that even returns a list of the results of each iteration: using this, a string reverse function can be had as a one-liner: Another example is the following range-aware switch variation. Tcl is no different. 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. The following "constructor" does that, plus it normalizes the signs, reduces to lowest terms, and returns just the integer n if d==1: Conversely, this "deconstructor" splits zero or more rational or integer strings into num and den variables, such that [ratsplit 1/3 a b] assigns 1 to a and 3 to b: Arithmetical helper functions can be wrapped with func if they only consist of one call of expr: Languages like Lisp and Python have the docstring feature, where a string in the beginning of a function can be retrieved for on-line (or printed) documentation. Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. A Functional Style and Its Algebra of Programs. Clif is the author of the TclTutor package2 and the books Tcl/Tk for Real Programmers and Tcl/Tk: A Developer's Guide3. Though slick at first sight, we actually have to type more. Tcl has no goto command, but it can easily be created. Before starting your programming, make sure you have one text editor in place and you have enough experience to write a computer program, save it in a file, build it, and finally execute it. Note that as my lmap above only takes one list, the two-list case had to be made explicit with foreach. But this version, that maps double first, works: One more experiment, just to get the feel: which gives 5.0. The balance of longer programs can be computed by just adding the balances of their individual bytecodes: The partitioning will run for some seconds (depending on nmax I tried with several ten thousand), but it's needed only once. If both the operands are non-zero, then condition becomes true. No con-/destructors are needed, in contrast to the heavierweight matrix in Tcllib. Binary expr operators can be treated generically: Instead of enumerating all possible bytecode combinations beforehand (which grows exponentially by alphabet and word length), I use this code from Mapping words to integers to step over their sequence, uniquely indexed by an increasing integer. For this, we reformat the expression to a list of values of type x or !x, that is in turn dumped into a local array for existence checking. following Backus' FP language with the "Def" command. But I notice more and more that, on my way to functional programming, my proc bodies are a single call to expr which does all the rest (often with the powerful x?y:z operator). Ah, the joys of weekend Tcl'ing and belatedly, Happy Birthday, John! Compared to an RPN language, hypot would be. In Europe and elsewhere, the most widely used paper format is called A4. 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