Assume variable A holds 1 and variable B holds 0, then . For this we again need a 1-based integer range generator: At this point, a number is prime if the sum of the latest vector is 2. Bertrand Russell commented that the author "has revealed a new calculus, of great power and simplicity" (somehow sounds like Tcl;^). 560 pages, Paperback. Bit vectors can also be used to indicate set membership (set operations would run faster if processing 32 bits on one go with bitwise operators (&, |, ~, ^)) or pixels in a binary imary image, where each row could be implemented by a bitvector. 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). 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. Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. Another example, cooked up by myself this time, computes the average of a list. Here's typical set operations. To find out how big a paper format is, one can measure an instance with a ruler, or look up appropriate documentation. 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). Here single bracing is correct. For instance, if the test has two inputs and wants one output, the stack balance is -1 (one less out than in). Factorial (n!) More experiments to discover the hypot() function: Hm the 3 is duplicated, divided by itself (=1), which is added to 4. 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. A math book showed me the Stirling approximation to n! 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). To make things easier, this flavor of "software" is in a very simple RPN language similar to, but much smaller than, the one presented in Playing bytecode: stack-oriented like Forth, each operation being one byte (ASCII char) wide, so we don't even need whitespace in between. ", 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). 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.. }. As a second step, we create the If command that wraps the expr invocation: This again passes impromptu tests, and adds the feature that any non-zero value counts as true and returns 1 if we neglect the other syntactic options of if, especially the elseif chaining. Another idea from SICP is a "smoothing" function, that averages each pair of values from the input stream. I added converters between characters and integers, and between strings and lists (see the dictionary below). Tk is an extension, developed by the creator of Tcl, used for creating scripts that interact with users through windows. 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. In these Tcl experiments, I use "" for "" and angle-brackets <> for the overbar-hook (with zero or more operands in between). It was created by John Osterhout in 1988. 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. #-- We can compute the modulo of a number by its index vector: #-- and turn all elements where the remainder is 0 to 1, else 0: #-- Hence, 7 is only divisible by 1 and itself, hence it is a prime. 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. 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. {AND, OR, NOT} resp. This makes sense, even in Tcl, where one might implement them as. 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. Compared to an RPN language, hypot would be. But for historical reasons, the Tcl command to create a function is called proc and thus people most often call them procedures. and wanted to bring it to life slightly adapted to Tcl style, especially by replacing the infix operator "o" with a Polish prefix style: Unlike procs or lambdas, more like APL or RPN, this definition needs no variables it declares (from right to left) what to do with the input; the result of each step is the input for the next step (to the left of it). Retrieving a record is as easy as this (though the fields come in undefined order): and deleting a record is only slightly more convolved: or, even easier and faster from Tcl 8.3 on: Here's how to get a "column", all fields of a given tag: But real columns may have empty fields, which we don't want to store. 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. Try to swap the inputs: Another dirty trick: get square root of 4, add to 3 presto, 5. The entire syntax of Tcl is described in just 12 rules. For creating FORTRAN and the BNF style of language description, he received the ACM Turing Award in 1977. All Exercises 122 Completed 0 In Progress 0 Available 122 Locked 0 Hello World Tutorial Exercise The classical introductory exercise. (I might have called it fun as well it sure is.) 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. However, most of these share the features. #-- Two abbreviations for frequently used list operations: #-- So let's try to implement "mean" in tacit Tcl! 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. All Tcl files will have an extension, i.e., .tcl. save it to a file for printing. Mathematically put. 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. But for n>143 we reach the domain limit of floating point numbers. On the other hand, Tk is a cross platform widget toolkit used for building GUI in many languages. Runtime of bit vector accesses is constant, except when a vector has to be extended to much larger length. 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! 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. 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. 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. A Functional Style and Its Algebra of Programs. This looks better to me than /slashing as in Postscript. It was first created by John Osterhout in 1989. #-- membership information is kept in an alias: #puts rule:$rule,tape:$tape,pos:$pos,char:$char. We still have the canonical truth values 0 and 1 as returned from expr with a comparison operator. This way, they are "pure values" and can be passed e.g. 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..). 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. in the forum The Tcl track on Exercism has Tcl is a powerful scripting language that runs under Unix, Linux, VMS, DOS/Windows, OS/2, and MacOS (at least). 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. Here is a routine for querying or setting single bits in vectors, where bits are addressed by non-negative integers. The following scripts are plain Tcl, they don't use the Tk GUI toolkit (there's a separate chapter for those). 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. Example: An existence map of ZIP codes between 00000 and 99999 can be kept in a list of 3125 integers (where each element requires about 15 bytes overall), while implementing the map as an array would take 100000 * 42 bytes in worst case, but still more than a bit vector if the population isn't extremely sparse in that case, a list of 1-bit positions, retrieved with lsearch, might be more efficient in memory usage. # This simple but infinite stream source produces all positive integers: # This produces all (well, very many) powers of 2: # A filter that reads and displays a stream until user stops it: # Here is a sample usage with famous name: #. which uses the (less) famous function maker: # Usage example: more {grep this {cat streams.tcl}}. 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. Such process chains can be emulated in Tcl with the following rules: A stream is modelled here as a procedure that returns one stream item on each call. In this article, we will know how to use procedures in TCL. Letter and Legal paper formats are popular in the US and other places. 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, " a" which by (4) means, "All kangaroos are avoided by me". Syntax: foreach var $Var_list { //operations for each $var } Example: for installation, user privileges, and system self-protection. 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. Tcl (Tool Command Language) is a very powerful but easy to learn dynamic programming language, suitable for a very wide range of uses, including web and desktop applications, networking, administration, testing and many more. Tcl is no different. In other words, a tautology. Note that on infinite streams, selectors may never return, e.g. It was then ported to Windows, DOS, OS/2, and Mac OSX. 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}. 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;-). They are however better reusable than the multable proc above. Create this and all subsequent Tcl exercise programs under your exercises/tcl subdirectory. Say you want to make a multiplication table for an elementary school kid near you. J's "from" operator { takes zero or more elements from a list, possibly repeatedly. 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. with automatic analysis 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. 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. The GOTO "jumping" instruction is considered harmful in programming for many years now, but still it might be interesting to experiment with. was instigated by the fact that in J, "NB." Classes in C++ started out as structs, so I take a minimal struct as example, with generic get and set methods. # 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. Getting more daring, let's try a distributive law: Daring more: what if we postulate the equivalence? 4. 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. The following example code opens a file, configures it to binary translation (i.e. In Tcl, a sensible implementation for compact data storage would be as a list of lists. The size of partitions is further reduced by excluding programs which contain redundant code, that will have no effect, like swapping the stack twice, or swapping before an addition or multiplication. 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. An obvious string representation of a rational is of course "n/d". 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 Another test, inequality: Trying to call 14 (OR) with more than two args: The constant 0 result is a subtle indication that we did something wrong:). 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". 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. In addition to extensive program-ming work on Tcl, Clif offers Tcl/Tk training sessions with in-class exercises. 123f.). Rules in this little challenge are of the form a bcD e, where, Here's my naive implementation, which takes the tape just as the string it initially is. 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. 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. Whether you need to automate repetitive behavior, extend the functionality of an application, control multiple tools with a single script or create a custom GUI, Tcl is your best choice. Rational numbers, a.k.a. The authors provide sample chapters available to download for free. 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. A collateral advantage is that all expressions are braced, without me having to care. 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. 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. Continuous, active development since the early 1990's. This way, a stream can promise to be a potentially endless source of data, while taking only finite time to process and deliver what's really wanted. Called Logical AND operator. That's all. But bare-bones has its advantages too: in order to see how a clockwork works, you'd better have all parts visible:). 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." 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. TCL Scripting Training. (!a || !b), but then again, these functions are equivalent. 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. * Edit and save ex1proc.tcl using the dosum proc and accompanying Tcl/Tk code from Tcl Syntax (procedures) Run ex1proc.tcl. through functions that take a table and return a table. 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. Just like functions, procedures take arguments and return some value. Especially, indexing the isa field allows iterating over "tables" (which we still don't explicitly have! to make it understand and do things that before raised an error, the easiest way is to write a proc. 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. personal mentoring, is used as comment indicator, both being well known Latin abbreviations: Again, the "->" argument is for eye-candy only but it feels better to me at least. They are for instance the building blocks of relational databases and spreadsheets. Called Logical OR Operator. More daring, let 's try to implement `` mean '' in tacit Tcl reach the limit! It was first created by John Osterhout in 1989 if we postulate the?... We postulate the equivalence grep this { cat streams.tcl } } $ }! 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