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. 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. 122 exercises Of course, with growing databases we may reach memory limits: arrays need some extra storage for administration. But bare-bones has its advantages too: in order to see how a clockwork works, you'd better have all parts visible:). $ mkdir ~/cs498gpl/exercises/tcl $ cd ~/cs498gpl/exercises/tcl. OK, I bite the bullet, set nmax to 500000, wait 5 minutes for the partitioning, and then: Hm.. cheap trick again it was discovered that the solution is just the successor of the second argument. 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 other words, a tautology. In the next step, I want to reimplement the "median" function, which for a sorted list returns the central element if its length is odd, or the mean of the two elements adjacent to the (virtual) center for even length. The know command is called with a condition that should result in an integer when given to expr, and a body that will be executed if cond results in nonzero, returning the last result if not terminated with an explicit return. (One might truncate the list at front if it gets too long). But if the database grows in size, it's a good idea to create indexes which cross-reference tags and values to IDs. Say you want to make a multiplication table for an elementary school kid near you. Here's my little take on toot in a nutshell. But for n>143 we reach the domain limit of floating point numbers. There are over 200 exercises with solutions for both Unix and Windows platforms. 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:-) }. Tcl/Tk for Programmers introduces high-level Tcl/Tk scripting language to experienced programmers with either Unix or Windows backgrounds. See all Tcl exercises Get started with the Tcl track The best part, it's 100% free for everyone. The Tcl track on Exercism has 122 exercises to help you write better code. Arguments are pushed on the stack, and the result of the "software", the stack at end, is returned. 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. 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). 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. Here we can do what we want, even retrieve which fields we have used so far (using a temporary array to keep track of field names): Searching for records that meet a certain condition can be done sequentially. It was then ported to Windows, DOS, OS/2, and Mac OSX. But this very soon crosses the limits of integers, giving wrong results. 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 in the forum The book includes a short introduction to TCP/IP, as well as longer introductions to writing client . Syntax: foreach var $Var_list { //operations for each $var } Example: This works fine on some well-known cryptarithms: There are lots of complex databases around. However, most of these share the features. 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? For porting this, lmap is a good helper, even though not strictly functional: We furtheron borrow some more content from expr: We'll need functional composition, and here's a recursive de-luxe version that takes zero or more functions, hence the name o*: is the neutral element of variadic functional composition, when called with no functions at all. Practical Programming in Tcl and Tk by Brent Welch, Ken Jones. This way, they are "pure values" and can be passed e.g. 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. Training will provide the detailed practical exposure on each aspect of project flow setup mostly focused on Physical Design, STA, and functional verification with multiple hands on examples. 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. 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. 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. Of course this is no real assembler. Elements are not removed by the popping, but (if necessary) when re-pushing. 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. 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;-). The other words (arguments) are not substituted because they're curly-braced, so either 0 or 1 is invoked, and does its simple job. So, on a morning dogwalk, I thought out this strategy: Here's this version. 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. The test suite at end should give many examples of what one can do in "r". I'm far from having digested it all, but like so often, interesting reading prompts me to do Tcl experiments, especially on weekends. 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. Rational numbers, a.k.a. and Insert is better known as fold, I suppose. 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. 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. 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). Tk is an extension, developed by the creator of Tcl, used for creating scripts that interact with users through windows. 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. Zimmer has extensive knowledge of Tcl/Tk programming and currently runs a consulting and training company based on his experience. The Tcl track on Exercism has This code for transposing a matrix uses the fact that variable names can be any string, including those that look like integers, so the column contents are collected into variables named 0 1 2 and finally turned into the result list: An integer range generator produces the variable names, e.g iota 3 => {0 1 2}. 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. The process of creating a simple database consists only of setting an initial value for the ID: Let's consider a library application for an example. All bits are initialized to 0. 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. Here is a routine for querying or setting single bits in vectors, where bits are addressed by non-negative integers. Discover new exercises as you progress and get engrossed in learning new concepts and improving the way you currently write. In that situation, you can fall back to the (otherwise slower, and uglier) use of a dedicated iterator: But neither can you filter the keys you will get with a glob pattern, nor may you add or delete array elements in the loop the search will be immediately terminated. Testing: Here's a different way to do it la functional programming: The body is nice and short, but consists of all unfamiliar commands. Creating a new syntax for a DSL would defeat the purpose of Tcl. in a priority queue, the object with the highest priority comes first. 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. Here's typical set operations. Clif first learned to program in high school in machine language on a Monroe 600 programmable . reports the results as wanted in the paper, on stdout: Streams are a powerful concept in (not only functional) programming. Maybe another weekend John Backus turned 80 these days. 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 (Comm. This simple example invokes expr if the "command" is digestible for it: Imagine the makers of Tcl had failed to provide the if command. 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 this article, we will know how to use procedures in TCL. Threads are for people who can't program state machines.". (I might have called it fun as well it sure is.) The GOTO "jumping" instruction is considered harmful in programming for many years now, but still it might be interesting to experiment with. 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. In SICP chapter 3.5, streams are introduced as data structures characterized as "delayed lists", whose elements are produced and returned only on demand (deferred evaluation). 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. 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). 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. 7. "Hello, World!" will get you writing some Tcl and familiarise yourself with the Exercism workflow. So an "assembler" program in this plaything will run even slower than in pure Tcl, and consume more memory while normally you associate speed and conciseness with "real" assembler code. 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. 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. to make it understand and do things that before raised an error, the easiest way is to write a proc. Other streams may provide a finite but very large number of elements, which would be impractical to process in one go. So, put the following source code in a test.tcl file. 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.
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