Discover new exercises as you progress and get engrossed in learning new concepts and improving the way you currently write. Functions in Tcl are typically written with the proc command. 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 and Insert is better known as fold, I suppose. It augments the current unknown code, at the top, with a handler for. if someone mentions its name (minibot), tries to parse the message and answer. Intro to Tcl: Exercises #2 Exercises #2 Rewrite the change function (Exercise 1.3) to work for any set of coins (or notes) for any decimal currency. The authors provide sample chapters available to download for free. Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. If bitval is given, sets the bit at numeric position position to 1 if bitval != 0, else to 0; in any case returns the bit value at specified position. (One might truncate the list at front if it gets too long). Task 1:- Input Output File Handling & Rearranging Data Step 1: Create a file and named it "file_input1.txt" (Content of "file_input1.txt" is given below - Remember, you have create file exactly same as given. true. Let's change that "a" can have only two values, "" or <>, so we might try to solve the expression by assuming all possible values for a, and see if they differ. The source files for Tcl programs are named with the extension ".tcl". priority queue is any of the more clever ways: A*, Greedy, builds up a nest of foreachs suiting the problem, quick kills (with continue) to force unique values for the variables, and. 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). Just like functions, procedures take arguments and return some value. Tables are understood here as rectangular (matrix) arrangements of data in rows (one row per "item"/"record") and columns (one column per "field"/"element"). Streams in general should not be written in brackets (then the Tcl parser would eagerly evaluate them before evaluating the command), but braced, and stream consumers eval the stream at their discretion. to make it understand and do things that before raised an error, the easiest way is to write a proc. Tcl was developed initially for Unix. Coroutines allow asynchronous interleaved tasks to be written in a sequential style. The idea in the paper I read is to use them as names of very simple functions: Glory be to the 11 rules of man Tcl that this is already a crude though sufficient reimplementation: The bracketed expr command is evaluated first, returning 0 or 1 as result of the comparison. A Functional Style and Its Algebra of Programs. Here's a little debugging helper, to find out why "know" conditions don't fire: Now testing what new magic this handful of code allows us to do. This page is not available in other languages. And that is one, and not the worst, Tcl way of Tacit programming APL and J (see Tacit programming) have the feature that arithmetics can be done with vectors and arrays as well as scalar numbers, in the varieties (for any operator @): Here's experiments how to do this in Tcl. . Here single bracing is correct. Tcl/Tk for Programmers is an introduction to the high-level Tcl/Tk scripting language for experienced programmers with either Unix or Windows background. This looks better to me than /slashing as in Postscript. 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. 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. 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. This result (0 or 1) is substituted for the first word of this command. Sorting can be done when pushing, or when popping, and since our push is so nicely generic I prefer the second choice (as the number of pushs and pops should be about equal, it does not really matter). Threads are for people who can't program state machines.". Tcl casts everything into the mold of a command, even programming constructs like variable assignment and procedure definition. Don't take this as a fundamental critique of Tcl, though its underlying model is far more simple and elegant than LISP's (what with "special forms", "reader macros"), and yet powerful enough to do just about everything possible which is sort of a mathematical thriller, if you will. For instance, if the test has two inputs and wants one output, the stack balance is -1 (one less out than in). Formally, what happened to the bracketed call is that it went through "applicative order" evaluation (i.e., do it now), while the braced commands wait for "normal order" evaluation (i.e., do when needed, maybe never the need is expressed through eval/upvar or similar commands). Hence, streams can be (and typically are) nested for processing purposes. Here are some Tcl codelets to demonstrate how all Boolean operations can be expressed in terms of the single NAND operator, which returns true if not both his two inputs are true (NOR would have done equally well). Indexes are useful for repeated information that is likely to be searched. Tcl/Tk for Programmers introduces high-level Tcl/Tk scripting language to experienced programmers with either Unix or Windows backgrounds. They are for instance the building blocks of relational databases and spreadsheets. * Edit and save ex1proc.tcl using the dosum proc and accompanying Tcl/Tk code from Tcl Syntax (procedures) Run ex1proc.tcl. In an RPN language, the example might look like this: which has the advantage that execution goes from left to right, but requires some stack awareness (and some swaps to set the stack right;^), Implementing Def, I took an easy route by just creating a proc that adds an argument and leaves it to the "functional" to do the right thing (with some quoting heaven:-) }. Should you need a unit matrix (where the main diagonal is 1, and the rest is 0), just call outProd with a different function (equality, ==): which just requires expr's equality to be exposed too: One of the fascinations of functional programming is that one can do the job in a simple and clear way (typically a one-liner), while using a collection of reusable building-blocks like lmap and iota. 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. 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. in state space searching, where the kind of container of the to-do list determines the strategy: Recent-use lists: A variation that can be used both in a stack or queue fashion is a list of values in order of their last use (which may come handy in an editor to display the last edited files, for instance). # - rewrite a proc's default arg with given value. See all Tcl exercises Get started with the Tcl track The best part, it's 100% free for everyone. Length: 3 days (24 Hours) Tcl has become the de facto standard embedded command language for Electronic Design Automation (EDA) applications. So, put the following source code in a test.tcl file. Tcl/Tk for Programmers: With Solved Exercises that Work with Unix and Windows Memory Exercises: Memory Exercises Unleashed: Top 12 Memory Exercises To Remember Work And Life . Only decades later, a hint in the Tcl chatroom pointed me to http://csc.smsu.edu/~shade/333/project.txt , an assignment to implement a Deterministic Turing Machine (i.e. We have the patron's and book's ID in variables and do double bookkeeping: When he returns the book, the process is reversed: The dueback field (%Y-%M-%d format is good for sorting and comparing) is useful for checking whether books have not been returned in time: Likewise, parts of the accounting (e.g. But if the database grows in size, it's a good idea to create indexes which cross-reference tags and values to IDs. It was then ported to Windows, DOS, OS/2, and Mac OSX. What's missing is the capability to randomly address parts of a stream, as is possible in Scheme (and of course their claim to do without assignment, or mutable data) Tcl lists just don't follow LISP's CAR/CDR model (though KBK demonstrated in Tcl and LISP that this structure can be emulated, also with procs), but rather C's flat *TclObject[] style. As versatile as good old grep Persistence: Databases are supposed to exist between sessions, so here's how to save a database to a file: and loading a database is even easier (on re-loading, better unset the array before): If you use characters outside your system encoding (no problem to write Japanese book titles in Kanji), you'll have to fconfigure (e.g -encoding utf-8) on saving and loading, but that's just a few more LOC. For instance, if you would like to simplify the for loop, for the typical simple cases so you can write instead. One point that was new for me is that the distinction between operators and operands is not cast in stone. So let's get the pieces together. Like in real life, test cases have to be carefully chosen. However, it fails to work if we add the successor of 0 as another test case: Nothing coming because zero division made the last test fail. 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. In J, it looks like this: which may better explain why I wouldn't want to code in J:^) J has ASCIIfied the zoo of APL strange character operators, at the cost of using braces and brackets as operators too, without regard for balancing, and extending them with dots and colons, so e.g. I rather wanted to explore some of these concepts and how to use them in Tcl, so that in slightly more verbose words I could code (and call). giving the correct result 2.5. Book . 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. 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. But the program "dd" (which just duplicates the top of stack twice) has a stack balance of +2, and hence can never pass the example test. For a real 8080, one would have to say. 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. all The print version is available from Amazon in USA/Canada and their European sites including UK , Germany , France , Spain and Italy . # make a list of 2**n lists, each with n truth values 0|1, #-- And here's some more hand-crafted bytecode implementations, #-- The stack routines imply a global stack::S, for simplicity, # a bytecode will consume at most two elements, #-- make a table of bytecode stack balances, #-- "peephole optimizer" - suppress code with redundancies. So 8 is the associated integer of a&&b, but not only of this we get the same integer for ! The entire syntax of Tcl is described in just 12 rules. "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. Tcl is a general purpose multi-paradigm system programming language. Here I want to explore how a database can be implemented in the Tcl spirit of simplicity, and how far that approach takes us. 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. Tcl/Tk for Programmers: With Solved Exercises that Work with Unix and Windows | Wiley Wiley : Individuals Shop Books Search By Subject Browse Textbooks Courseware WileyPLUS Knewton Alta zyBooks Test Prep (View All) CPA Review Courses CFA Program Courses CMA Exam Courses CMT Review Courses Brands And Imprints (View All) Dummies JK Lasser It was created by John Osterhout in 1988. 7. The other words (arguments) are not substituted because they're curly-braced, so either 0 or 1 is invoked, and does its simple job. Without proof, I just claim that every function of n arguments whose characteristic integer is 2^(2^n) 1 is a tautology (or a true statement all bits are 1). If they don't, we have found a fact that isn't dependent on the variable's value, and the resulting constant is returned, otherwise the unsolved expression: with a helper function in that reports containment of an element in a list: which means, in expr terms, {(!$a || $a) == 1}, for all values of a. Chapter 4 discusses Tcl I/O support for les, pipes, and sockets. Here is a simple example of a "chat bot" a program that listens on an IRC chatroom, and sometimes also says something, according to its programming. A matter of style and taste, in a way multable is 10 LOC and depends on nothing but Tcl, which is good; multable2 describes quite concisely what it does, and builds on a few other procs that are highly reusable. Following table shows all the logical operators supported by Tcl language. Another example is this integer range generator (starts from 1, and is inclusive, so [iota1 5] == {1 2 3 4 5}): "NAND is not AND." Note however that you need stdin for this implementation, which excludes wishes on Windows (one might easily write a UI-more that reacts on mouse clicks, though). This makes sense, even in Tcl, where one might implement them as. Here's typical set operations. Retrieving fields that may not physically exist needs a tolerant access function: In a classical database we have to define tables: which fields of what type and of which width. Ah, the joys of weekend Tcl'ing and belatedly, Happy Birthday, John! This idea may have been first brought up in Functional programming (Backus 1977), if not in Forth and Joy, and it's an interesting simplification compared to the lambda calculus. So I tried with another a^2+b^2=c^2 set, and HEUREKA! In addition, for all procs, even without docstring, you get the "signature" (proc name and arguments with defaults). A range (numeric or strings) can be given as from..to, and the associated scriptlet gets executed if the tested value lies inside that range. There are over 200 exercises with solutions that run on both Unix and Windows platforms. 100% free. 122 exercises #-- Two abbreviations for frequently used list operations: #-- So let's try to implement "mean" in tacit Tcl! Doing more steps towards functional programming, I came upon this interesting problem, and will shortly demonstrate that it can easily be solved in pure-Tcl. As everything is a string, and to Tcl "a" is {a} is a , Joy's polymorphy has to be made explicit. 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