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. (after 286 seconds): After partitioning, 54005 programs had the -1 stack balance, and the correct result was on position 48393 in that list And finally, with the half-million set of programs, here's a solution for the successor function too: "d-" subtracts top of stack from itself, pushing 0; the second duplicate to the 0-th power gives 1, which is added to the original argument. Procedures are just like functions we use in any other programming language such as C, Java, Python, etc. 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). OO (Object Orientation) is a style in programming languages popular since Smalltalk, and especially C++, Java, etc. It was created by John Osterhout in 1988. 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. First lmap is a collecting foreach it maps the specified body over a list: The following generic wrapper takes one binary operator (could be any suitable function) and two arguments, which may be scalars, vectors, or even matrices (lists of lists), as it recurses as often as needed. The print version is available from Amazon in USA/Canada and their European sites including UK , Germany , France , Spain and Italy . all 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. For clearer code, it is advisable to factor out frequent operations into procs, e.g. Genres Programming. For creating FORTRAN and the BNF style of language description, he received the ACM Turing Award in 1977. 123f.). The following scripts are plain Tcl, they don't use the Tk GUI toolkit (there's a separate chapter for those). On the other hand, Tk is a cross platform widget toolkit used for building GUI in many languages. #-- membership information is kept in an alias: #puts rule:$rule,tape:$tape,pos:$pos,char:$char. Tcl/Tk 8.2.3 and Tcl/Tk 8.3.0 under windows. To find out how big a paper format is, one can measure an instance with a ruler, or look up appropriate documentation. Core Python Programming, chapter 5 exercises number 5-3, question on this exercise. 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. If both the operands are non-zero, then condition becomes true. more is the most important "end-user" of streams, especially if they are infinite. 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". 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). As everything is a string, and to Tcl "a" is {a} is a , Joy's polymorphy has to be made explicit. 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. Getting more daring, let's try a distributive law: Daring more: what if we postulate the equivalence? Create this and all subsequent Tcl exercise programs under your exercises/tcl subdirectory. But if the database grows in size, it's a good idea to create indexes which cross-reference tags and values to IDs. 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. 122 exercises to help you write better code. (I used uplevel instead of eval to keep all side effects in caller's scope). TCL Scripting Training. The special item "" (the empty string) indicates that the stream is exhausted. Book . For Joy's sets I haven't bothered yet they are restricted to the domain 0..31, probably implemented with bits in a 32-bit word. with our unique blend of learning, practice and mentoring. 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). Tcl is a scripting language somewhat like Perl but extensible and clearer. 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. 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. 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 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. 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. Tables are understood here as rectangular (matrix) arrangements of data in rows (one row per "item"/"record") and columns (one column per "field"/"element"). }. of your code and Here is a simpler way that allows to extend unknown "in place" and incrementally: We let unknown "know" what action it shall take under what conditions. 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. 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). 4. The first formats a matrix (a list of lists to Tcl) with newlines and aligned columns for better display: Short again, and slightly cryptic, as is the "outer product" routine, which takes a function f and two vectors, and produces a matrix where f was applied to every pair of a x b in APL they had special compound operators for this job, in this case ".x": Again, lmap (the collecting foreach) figures prominently, so here it is in all its simplicity: With these parts in place, we can see that multable2 works as we want: So why write six procedures, where one did the job already? Like in switch, fall-through collapsing of several cases is indicated by "-", and "default" as final condition fires if none else did. 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. {&&, ||,! 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.. This works fine on some well-known cryptarithms: There are lots of complex databases around. Of course, with growing databases we may reach memory limits: arrays need some extra storage for administration. 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). 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. But bare-bones has its advantages too: in order to see how a clockwork works, you'd better have all parts visible:). Tcl/Tk for Programmers is an introduction to the high-level Tcl/Tk scripting language for experienced programmers with either Unix or Windows background. 100% free, forever. Tcl 8.5 Network Programming (2010) , by Kocjan and Beltowski, is targeted towards building network-aware applications using Tcl and includes coverage of many Tcl libraries and extensions. In a nutshell, his FP system comprises. ): proc flatten_list { l } { if { [llength $l] == 0 } { return {} } elseif { [llength $l] == 1 && [lindex $l 0] == $l } { return $l } else { set ret {} 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. in the forum Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. "Hello, World!" will get you writing some Tcl and familiarise yourself with the Exercism workflow. Tcl is a popular and widely used cross-platform script programming language that achieves significant productivity gains when used by skilled engineers. Now we can write n(f), which, given a Boolean function of one or more arguments, returns its characteristic number, by iterating over all cases in the truth table, and setting a bit where appropriate: So the characteristic integer is not the same as the Goedel number of a function, which would encode the structure of operators used there. Tcl's lists are well suited to represent sets. Chapter 4 discusses Tcl I/O support for les, pipes, and sockets. 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). 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 chapter provides an overview of the Tcl syntax, data structures, and enough commands to develop applications. 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). Tcl is no different. The numbers of the bits finally still set are supposed to be primes, and returned: Here's code to count the number of 1-bits in a bit vector, represented as an integer list. "Hello, World!" is the traditional first program for beginning programming in a new language or environment. Factorial (n!) Let us write a simple Tcl program. Ramanujan numbers: The pairs generator can be used to find Ramanujan numbers, which can be represented as the sum of two integer cubes in more than one way. 5. converting Java app to Tcl/Tk ( new thread for all the tcl/tk itcl gurus) 6. Nth Prime In a very radical simplification, a whole world is built up by two operators, juxtaposition without visible symbol (which could be likened to or) and a overbar-hook (with the meaning of not) that I can't type here it's a horizontal stroke over zero or more operands, continued at right by a vertical stroke going down to the baseline. execution of the script "++" should sum its three arguments (1+(2+3)), and return 6. Tcl is a high-level language well suited for rapid development and prototyping. For instance, if the test has two inputs and wants one output, the stack balance is -1 (one less out than in). Since the pseudo-register M can also be used for writing back, it cannot be implemented by simply copying the value. 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. 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. Rational numbers, a.k.a. 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? Here I want to explore how a database can be implemented in the Tcl spirit of simplicity, and how far that approach takes us. I know there are many table implementations in Tcl, but like so often I wanted to build one "with my bare hands" and as simple as possible. This page was last edited on 16 April 2020, at 06:44. The authors provide sample chapters available to download for free. 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). The set of all defined bytecodes will be the alphabet of this little RPN language. # predecessor function, when for integers. Tests are done with this minimal "framework": The dot product of two vectors is a scalar. In truly brute force, up to half a million programs are automatically written and (a suitable subset of them) tested to find the one that passes the tests. 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. Tcl provides the syntax so that the DSL designer can focus on the grammar. {AND, OR, NOT} resp. The following "General Problem Solver" (for small values of General) uses heavy metaprogramming: it. The other words (arguments) are not substituted because they're curly-braced, so either 0 or 1 is invoked, and does its simple job. 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. Runtime of bit vector accesses is constant, except when a vector has to be extended to much larger length. In fact, the float limit is at n>170, so an intermediate result in the Stirling formula must have busted at 144. in a priority queue, the object with the highest priority comes first. But this version, that maps double first, works: One more experiment, just to get the feel: which gives 5.0. This means that subsequent calls to know stack up, last condition being tried first, so if you have several conditions that fire on the same input, let them be "known" from generic to specific. A more generic filter takes a condition and a stream, and on each call returns an element of the input stream where the condition holds if ever one comes along: Friends of syntactic sugar might prefer shell style: and guess what, we can have that in Tcl too (and not in Scheme!-), by writing a proc, that also resets all sprocs, with the fancy name "$" (in Unix, this could be the shell prompt that you don't type, but for Tcl we always have to have the command name as first word): To prove that we haven't cheated by using exec, let's introduce a line counter filter: This can be added to filter chains, to count lines in the original file, or only the results from grep: We further observe that more has a similar structure to filter, so we could also rewrite it in terms of that: The sort filter is unusual in that it consumes its whole (finite!) Maybe another weekend John Backus turned 80 these days. In addition to extensive program-ming work on Tcl, Clif offers Tcl/Tk training sessions with in-class exercises. 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. save it to a file for printing. 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: }. Bertrand Russell commented that the author "has revealed a new calculus, of great power and simplicity" (somehow sounds like Tcl;^). Here's the "bytecode engine" (ebc: execute byte code), which retrieves the implementations of bytecodes from the global array cmd: Let's now populate the bytecode collection. 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". No con-/destructors are needed, in contrast to the heavierweight matrix in Tcllib. Procedural, OO, functional; builtin event loop for network programming and asynchronous file I/O. 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. 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. 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. Learning Objectives The first two days of this course provide a . in static variables (here implemented with the fancy remember proc) examples are intgen that delivers ever increasing integers, or gets $fp where the file pointer advances at each call, so potentially all lines of the file are returned over time. To extend Tcl, i.e. The book includes a short introduction to TCP/IP, as well as longer introductions to writing client . Different from switch, numbers are compared by numeric value, no matter whether given as decimal, octal or hex. If they don't, we have found a fact that isn't dependent on the variable's value, and the resulting constant is returned, otherwise the unsolved expression: with a helper function in that reports containment of an element in a list: which means, in expr terms, {(!$a || $a) == 1}, for all values of a. 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. This looks better to me than /slashing as in Postscript. It includes a short introduction to TCP/IP, introductions on writing client-side scripts and GUI interfaces as well as integrating scripts with C/C++. However, as integer division takes place, it would be better to make that. #-- Two abbreviations for frequently used list operations: #-- So let's try to implement "mean" in tacit Tcl! So, put the following source code in a test.tcl file. This can be plugged into a filter chain to see what's going on: # or, to get a stream of even numbers, starting from 0: "to recall is to call -- (1 || 1) == 1", "PONG [info hostname] [lindex [split $line] 1]", "Try http://wiki.tcl.tk/[lindex $args end]", "Why do [string map {I you my your your my you me} $args]? for installation, user privileges, and system self-protection. 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. They're great practice and fun to do! Tcl supports multiple programming paradigms, including object-oriented . 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. But for historical reasons, the Tcl command to create a function is called proc and thus people most often call them procedures. Most of these example scripts first appeared in the Tclers' Wiki http://wiki.tcl.tk . There are over 200 exercises with solutions for both Unix and Windows platforms. The correct hypot() function would be. 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. 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. Tk is an extension, developed by the creator of Tcl, used for creating scripts that interact with users through windows. 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. All bits are initialized to 0. They are for instance the building blocks of relational databases and spreadsheets. 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. In Europe and elsewhere, the most widely used paper format is called A4. For easier handling, it's a good idea to classify records somehow (we'll want to store more than books), so we add. 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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