For easier handling, it's a good idea to classify records somehow (we'll want to store more than books), so we add. 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". Though slick at first sight, we actually have to type more. The task is to conclude something from the following premises: These are encoded to the following one-letter predicates: So the problem set can be restated, in Spencer-Brown's terms, as. Threads are for people who can't program state machines.". It augments the current unknown code, at the top, with a handler for. Exercise 1 - Tcl procedure. 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. #puts "$mem($pc)\tA:$::A B:$::B C:$::C D:$::D E:$::E Z:$::Z", #----------------- "machine opcodes" implemented as procs, ; idiomatic: get over the initial variable(s), ; load double registers H+L with the address INCR, ; load byte to register B from the address pointed to in HL, "$body \$x [string repeat \] [llength $args]]". 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 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). For creating FORTRAN and the BNF style of language description, he received the ACM Turing Award in 1977. The pattern, is a kind of conditional in J, which could in Tcl be written. 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:). First published January 1, 1998. All Tcl files will have an extension, i.e., .tcl. So what about a thin abstraction (wrapper) around this recurring pattern? 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 There are over 200 exercises with solutions for both Unix and Windows platforms. But this very soon crosses the limits of integers, giving wrong results. Tcl/Tk for Programmers introduces high-level Tcl/Tk scripting language to experienced programmers with either Unix or Windows backgrounds. The book includes a short introduction to TCP/IP, as well as longer introductions to writing client . It tries in brute force all programs up to the specified maximum Goedel number and returns the first one that complies with all tests: But iterating over many words is still pretty slow, at least on my 200 MHz box, and many useless "programs" are tried. 5. converting Java app to Tcl/Tk ( new thread for all the tcl/tk itcl gurus) 6. Rather, one could use read and write traces on variable M, causing it to load from, or store to, mem($HL). Tcl's lists are well suited to represent sets. "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. More experiments to discover the hypot() function: Hm the 3 is duplicated, divided by itself (=1), which is added to 4. 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. 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. This page is not available in other languages. Tcl is a scripting language somewhat like Perl but extensible and clearer. The absence of lexical scoping also led to constructs like sproc/reset, which stop a gap but aren't exactly elegant but Tcl's clear line between either local or global variables allows something like closures only by rewriting default arguments like done in remember (or like in Python). 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. Rational numbers, a.k.a. The memory model is constant-size instructions (strings in array elements), which are implemented as Tcl procs. The authors provide sample chapters available to download for free. So here is one model of a state machine in ten lines of code. Learning Objectives The first two days of this course provide a . "{usage: $procname [uplevel 1 [list info args $procname]]}", # This comment should not appear in the docstring, # Signature of a proc: arguments with defaults, # fall back to standard queue, now that it's sorted, "foreach $var \$domain[expr [lsearch $initials $var]>=0] \{\n", "if {\[expr $test\]} {return \[subst $test\]}", "[db'get db $id author]: [db'get db $id title] $db($i)", "please return $db($book,title) which was due on\, "[db'get db $id title] - [db'get db $id label]". The GOTO "jumping" instruction is considered harmful in programming for many years now, but still it might be interesting to experiment with. But this version, that maps double first, works: One more experiment, just to get the feel: which gives 5.0. 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. more is the most important "end-user" of streams, especially if they are infinite. The cute name "e.g." 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. 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:-) }. In Tcl, a sensible implementation for compact data storage would be as a list of lists. Creating a new syntax for a DSL would defeat the purpose of Tcl. 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. A Functional Style and Its Algebra of Programs. For instance, if you would like to simplify the for loop, for the typical simple cases so you can write instead. line-ends \r\n are not standardized to \n as usual in C), and prints as many lines as needed which each contain 16 bytes in hexadecimal notation, plus, where possible, the ASCII character. 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. Tcl is available for Linux, Windows, Mac OS X, as well as other platforms, as open-source software under BSD-like license, or as pre-built binaries. 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. Syntax: foreach var $Var_list { //operations for each $var } Example: 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 "main routine" is a single line that dumps all files given on the command line: Sample output, the script applied to itself: Roman numerals are an additive (and partially subtractive) system with the following letter values: Here's some Tcl routines for dealing with Roman numerals. # Multiple documentation lines are allowed. 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. The purpose of developing this language is easy embedded inti ( ) applications. Note that on infinite streams, selectors may never return, e.g. 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. 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. (I used uplevel instead of eval to keep all side effects in caller's scope). 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. 100% free. This chapter provides an overview of the Tcl syntax, data structures, and enough commands to develop applications. Tcl is a powerful scripting language that runs under Unix, Linux, VMS, DOS/Windows, OS/2, and MacOS (at least). Tcl provides the syntax so that the DSL designer can focus on the grammar. 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. See all Tcl exercises Get started with the Tcl track The best part, it's 100% free for everyone. by one the binary operators +-*/. Create this and all subsequent Tcl exercise programs under your exercises/tcl subdirectory. For instance, if the test has two inputs and wants one output, the stack balance is -1 (one less out than in). Here's typical set operations. all 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. 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. 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. 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. The ebook version (PDF format) is available from Gumroad .. Implement an evaluator for a very simple subset of Forth. Tcl is a string based scripting language. 123f.). The following "General Problem Solver" (for small values of General) uses heavy metaprogramming: it. 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} $args]? giving the correct result 2.5. #-- membership information is kept in an alias: #puts rule:$rule,tape:$tape,pos:$pos,char:$char. ", http://csc.smsu.edu/~shade/333/project.txt, https://en.wikibooks.org/w/index.php?title=Tcl_Programming/Examples&oldid=3678753, Common Lisp: (documentation 'foo 'function), The ratio between the longer and the shorter side of an A format is constant, pop: retrieve and remove one object from the container, in a stack, the most recently pushed object is retrieved and removed (last in first out, LIFO), in a (normal) queue, it is the least recently pushed object (first in first out, FIFO). 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. From Grade School to Raindrops. This page was last edited on 16 April 2020, at 06:44. 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. The source files for Tcl programs are named with the extension ".tcl". They always return a result (even if it is the empty string ""), so to call them functions might be most appropriate. 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. Here's our recommended free books that'll help you master Tcl. }, Test data from http://csc.smsu.edu/~shade/333/project.txt. They think it's a programing (like software programing) and they are in VLSI Industry to do some hardware related job. # This filter collects its input (should be finite;-) into a list: # $ streamlist {foo bar grill a} | sort | collect => a bar foo grill. . In these Tcl experiments, I use "" for "" and angle-brackets <> for the overbar-hook (with zero or more operands in between). Of course this is no real assembler. 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). The Tcl track on Exercism has In both cond and body you may use the variable args that holds the problem command unknown was invoked with. Tcl was designed for creating domain-specific languages. so the two-way If is about as mighty as the real thing, give or take a few braces and redundant keywords (then, else). Its combination of text processing, file manipulation and system control features make it ideal for this purpose. 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). I started with Backus' first Functional Program example. # - rewrite a proc's default arg with given value. For clearer code, it is advisable to factor out frequent operations into procs, e.g. Tcl is a scripting language somewhat like Perl but extensible and clearer. It was then ported to Windows, DOS, OS/2, and Mac OSX. The extending code what is prepended to the previous unknown body. Note that +/ is considered one operator, which applies the "adverb" folding to the "verb" addition (one might well call it "sum"). 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. 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. 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. Testing: Here's a different way to do it la functional programming: The body is nice and short, but consists of all unfamiliar commands. personal mentoring, But if the database grows in size, it's a good idea to create indexes which cross-reference tags and values to IDs. 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. To extend Tcl, i.e. 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. Write a function to determine if a list is a sublist of another list. Of course I can't use circumfix brackets as operator name, so let's call it constr: which returns correctly 3. and let's discuss it. 1. foreach loop Use: Where we have to iterate on each element on a list of elements and have to perform some operation on each element. which, when called with no arguments, return 1 or 0, respectively. Running a Tcl/Tk applet within a Tcl/Tk program. to make it understand and do things that before raised an error, the easiest way is to write a proc. 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. The source code is compiled into bytecode, which is later interpreted by the Tcl interpreter. 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. However, this is no fundamental problem consider that. We still have the canonical truth values 0 and 1 as returned from expr with a comparison operator. #-- Move tape Left or Right as specified in rule. with automatic analysis ACM 21.8, Aug. 1978, 613-641), he developed an amazing framework for functional programming, from theoretical foundations to implementation hints, e.g. Tests are done with this minimal "framework": The dot product of two vectors is a scalar. To find out how big a paper format is, one can measure an instance with a ruler, or look up appropriate documentation. 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 we can also multiply out the 1s with the divisors from the i ndex vector: So 6 is divisible by 2 and 3; non-zero elements in (lrange $divisors 1 end-1) gives the "proper" divisors. If a filter meets end-of-stream, it should return that too. 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). 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. Most of these example scripts first appeared in the Tclers' Wiki http://wiki.tcl.tk . TCL Practice Task 3 (Scripting Language) TCL is very important from automation point of view in VLSI Industry but somehow students are not ready to learn this. This is something like the Goedel number of the corresponding code. Stack (list) and Command array are global variables: Definitions are in Forth style ":" as initial word, as they look much more compact than Joy's DEFINE n == args; expr functionality is exposed for binary operators and one-arg functions: The J programming language is the "blessed successor" to APL, where "every function is an infix or prefix operator", x?y (dyadic) or ?y (monadic), for ? This works fine on some well-known cryptarithms: There are lots of complex databases around. #-- This "functional form" is mostly called map in more recent FP: #-- Prefix multiplication comes as a special case of this: "if {\[$condition \$x\]} {$function \$x} else", #-- Testing, with K in another role as Konstant function:). Genres Programming. Indexes: As shown, we can retrieve all data by sequential searching over array names. There are over 200 exercises with solutions that run on both Unix and Windows platforms. 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. 71 coding exercises for C on Exercism. Make sure the fields (cells) match those in the header. Practical Programming in Tcl and Tk by Brent Welch, Ken Jones. The goto command is defined "locally", and deleted after leaving the state machine it is not meaningfully used outside of it. 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. Called Logical OR Operator. 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). if someone mentions its name (minibot), tries to parse the message and answer. Tcl/Tk for Programmers is an introduction to the high-level Tcl/Tk scripting language for experienced programmers with either Unix or Windows background. Streams are interesting if they don't deliver the same result on every call, which requires them to maintain state between calls e.g. As everything is a string, and to Tcl "a" is {a} is a , Joy's polymorphy has to be made explicit. 1. 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). Execution starts at the first of the states. 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. Chapters 5-8 introduce more commands and techniques and A math book showed me the Stirling approximation to n! Functions in Tcl are typically written with the proc command. (!a || !b), but then again, these functions are equivalent. 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. Procedural, OO, functional; builtin event loop for network programming and asynchronous file I/O. Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. 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. 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. Single bytecodes are executed, only to measure their effect on the stack. Tables are understood here as rectangular (matrix) arrangements of data in rows (one row per "item"/"record") and columns (one column per "field"/"element"). 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. ; s our recommended free books that tcl programming exercises # x27 ; s our recommended free books that & # ;! Is available from Gumroad previous unknown body a sublist of another list, wrong. 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