#--Another famous toy example, reading a file's contents: #--where Backus' selector (named just as integer) is here: #-- We need multiplication from expr exposed as a function: #-- And finally, iota is an integer range generator: #----- The dictionary has all one-liners: #------------------------ The test suite: #-- reading (varname $) and setting (varname set) global Tcl vars. Adding a book to the database can be simply done by, Note that, as we never specified what fields a record shall contain, we can add whatever we see fit. In TOOT, the values of objects are represented as a list of length 3: the class name (so much for "runtime type information":-), a "|" as separator and indicator, and the values of the object, e.g. 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." # Multiple documentation lines are allowed. 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. Any proc must however be called in compliance with Tcl's fundamental syntax: first word is the command name, then the arguments separated by whitespace. The author (Richard Suchenwirth) declares them to be fully in the public domain. A program without such extravaganzas is shorter and yet does the same job, so it will have been tested earlier anyway. 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. Saving also goes a good way to what is ceremonially called "committing" (you'll need write-locking for multi-user systems), while loading (without saving before) might be called a "one-level rollback", where you want to discard your latest changes. The Tcl track on Exercism has On the other hand, the present approach is pretty economic, since it does not use field widths (all strings are "shrink-wrapped"), and omits empty fields, while at the same time allowing to add whatever fields you wish. # 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. In the algebra introduced here, with a variable "a", no further simplification was so far possible. Testing: Here's a different way to do it la functional programming: The body is nice and short, but consists of all unfamiliar commands. A filter takes one or more streams, and possibly other arguments, and reacts like a stream too. one with at most one rule per state and input character), which gives clear instructions and two test cases for input and output, so I decided to try my hand in 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. This page is not available in other languages. Tcl is a high-level language well suited for rapid development and prototyping. Note that on infinite streams, selectors may never return, e.g. Indexes: As shown, we can retrieve all data by sequential searching over array names. But for n>143 we reach the domain limit of floating point numbers. 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. In the opposite direction, we can call a Boolean function by its number and provide one or more arguments if we give more than the function can make sense of, non-false excess arguments lead to constant falsity, as the integer can be considered zero-extended: So f(n) 14 indeed behaves like the OR function little surprise, as its truth table (the results of the four calls), read bottom-up, 1110, is decimal 14 (8 + 4 + 2). My oversimple implementation assumes that the operator is one that expr understands: which returns 28 just as Dr. Backus ordered (= 1*6 + 2*5 + 3*4). 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. Start a new topic As everything is a string, and to Tcl "a" is {a} is a , Joy's polymorphy has to be made explicit. 122 exercises to help you write better code. execution of the script "++" should sum its three arguments (1+(2+3)), and return 6. All Exercises 122 Completed 0 In Progress 0 Available 122 Locked 0 Hello World Tutorial Exercise The classical introductory exercise. The pattern, is a kind of conditional in J, which could in Tcl be written. See all Tcl exercises Get started with the Tcl track The best part, it's 100% free for everyone. Implement an evaluator for a very simple subset of Forth. Testing early and often is a virtue, as is documentation to make the following code snippets clearer, I tuned my little tester for better looks, so that the test cases in the source code also serve as well readable examples they look like comments but are code! in static variables (here implemented with the fancy remember proc) examples are intgen that delivers ever increasing integers, or gets $fp where the file pointer advances at each call, so potentially all lines of the file are returned over time. 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). In Spencer-Brown's terms, [] (which is "", the empty string with no arguments) is false ("nil" in LISP), and [<>] is the negation of "", i.e. Filters may be characterized as "selectors" (who may return only part of their input, like "grep") and/or "appliers" who call a command on their input and return the result. In addition to extensive program-ming work on Tcl, Clif offers Tcl/Tk training sessions with in-class exercises. * Edit and save ex1proc.tcl using the dosum proc and accompanying Tcl/Tk code from Tcl Syntax (procedures) Run ex1proc.tcl. Clif first learned to program in high school in machine language on a Monroe 600 programmable . 71 coding exercises for C on Exercism. Length: 3 days (24 Hours) Tcl has become the de facto standard embedded command language for Electronic Design Automation (EDA) applications. Deeper changes are possible with the unknown command, which is called if a command name is, well, unknown, and in the standard version tries to call executables, to auto-load scripts, or do other helpful things (see the file init.tcl). A simpler example is pipes in Unix/DOS (use TYPE for cat there): where the "cat" delivers lines of the file as long as "more" will take them, and waits otherwise (after all, stdin and stdout are just streams). The following example code opens a file, configures it to binary translation (i.e. 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. 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 it looks halfway like the real thing: you get sort of an assembly listing with symbol table, and can run it I'd hardly start writing an assembler in C, but in Tcl it's fun for a sunny Sunday afternoon }, The mov b,INCR part is an oversimplification. If you use the tiny testing framework explained earlier, the e.g. This way, they are "pure values" and can be passed e.g. Core Python Programming, chapter 5 exercises number 5-3, question on this exercise. In his Turing Award lecture, Can Programming Be Liberated from the von Neumann Style? Tcl/Tk for Programmers is an introduction to the high-level Tcl/Tk scripting language for experienced programmers with either Unix or Windows background. Enrol for e-learning course for self paced learning. Live Demo #!/usr/bin/tclsh puts "Hello, World!" Assuming, Tcl environment is setup correctly; let's run the program after switching to file's directory and then execute the program using $ tclsh test.tcl with our unique blend of learning, practice and mentoring. 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. Functions in Tcl are typically written with the proc command. They are for instance the building blocks of relational databases and spreadsheets. The discoverer, Second Edition, determines the stack balance of the first text, and tests only those programs of the same partition: But now for the trying. 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. 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. 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. # This filter collects its input (should be finite;-) into a list: # $ streamlist {foo bar grill a} | sort | collect => a bar foo grill. Learning Objectives The first two days of this course provide a . 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. 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). I started with Backus' first Functional Program example. Tcl - Environment Setup . Explore the Tcl exercises on Exercism Unlock more exercises as you progress. Another example, cooked up by myself this time, computes the average of a list. giving the correct result 2.5. Called Logical AND operator. TCL is shell application that reads TCL command from its standard input or from a file and gives desired results. Bertrand Russell commented that the author "has revealed a new calculus, of great power and simplicity" (somehow sounds like Tcl;^). 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. 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). 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. The memory model is constant-size instructions (strings in array elements), which are implemented as Tcl procs. Unlike in earlier years when I was playing APL, this time my aim was not to parse and emulate J in Tcl I expected hard work for a dubitable gain, and this is a weekend fun project after all. Here single bracing is correct. The toplevel proc takes a paired list of inputs and expected output. "Hello, World!" is the traditional first program for beginning programming in a new language or environment. In Tcl, the two ways of reading a file are a good example: The second construct may be less efficient, but is robust for gigabyte-sized files. Of course I can't use circumfix brackets as operator name, so let's call it constr: which returns correctly 3. 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. The set of all defined bytecodes will be the alphabet of this little RPN language. 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). of your code and J's "from" operator { takes zero or more elements from a list, possibly repeatedly. by one the binary operators +-*/. Continuous, active development since the early 1990's. Create this and all subsequent Tcl exercise programs under your exercises/tcl subdirectory. Introduction to the Tcl 3 Language The next ve chapters constitute a Tcl language tutorial. # predecessor function, when for integers. The first and second arguments are the class (disregarded here, as the dash shows) and the value, the rest is up to the coder. Like in switch, fall-through collapsing of several cases is indicated by "-", and "default" as final condition fires if none else did. This may be used for Boolean properties of numerically indexed sets of items. The cute name "e.g." 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. Tcl is used for web applications, desktop GUIs, testing and automation, and more. The Tcl Programming Language is a comprehensive guide to Tcl, covering Tcl 8.6.. See the official book page for more information and a detailed Table of Contents.. Here, pushing has to be done by dedicated code because a previous instance would have to be removed: The first element is the least recently, the last the most recently used. so the two-way If is about as mighty as the real thing, give or take a few braces and redundant keywords (then, else). 2. looking for: Tcl/Tk exercises (please) 3. Tcl provides the syntax so that the DSL designer can focus on the grammar. And when both x and !x exist, they are removed from the expression: translated back: "I avoid it, or it's not a kangaroo", or, reordered, "
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