560 pages, Paperback. "{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]". Runtime of bit vector accesses is constant, except when a vector has to be extended to much larger length. 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. 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. 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. The ebook version (PDF format) is available from Gumroad .. {&&, ||,! bit foo 32 will turn foo into a list of two integers, if it was only one before. 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. Tcl is a general purpose multi-paradigm system programming language. Develop fluency in 67 programming languages # This filter collects its input (should be finite;-) into a list: # $ streamlist {foo bar grill a} | sort | collect => a bar foo grill. is a popular function with super-exponential growth. 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. Elements are not removed by the popping, but (if necessary) when re-pushing. A very simple control structure (one might also call it a result dispatcher) is the K combinator, which is almost terribly simple: It can be used in all situations where you want to deliver a result that is not the last. Just say "Hello, World!". 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. Zimmer has extensive knowledge of Tcl/Tk programming and currently runs a consulting and training company based on his experience. Indexes are useful for repeated information that is likely to be searched. Tcl is a scripting language somewhat like Perl but extensible and clearer. 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. #-- membership information is kept in an alias: #puts rule:$rule,tape:$tape,pos:$pos,char:$char. Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. The book includes a short introduction to TCP/IP, as well as longer introductions to writing client . Especially, indexing the isa field allows iterating over "tables" (which we still don't explicitly have! All Tcl files will have an extension, i.e., .tcl. The special item "" (the empty string) indicates that the stream is exhausted. The first and second arguments are the class (disregarded here, as the dash shows) and the value, the rest is up to the coder. 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. 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. Classes in C++ started out as structs, so I take a minimal struct as example, with generic get and set methods. 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. 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. If any of the two operands is non-zero, then . In Tcl, a sensible implementation for compact data storage would be as a list of lists. if someone mentions its name (minibot), tries to parse the message and answer. # That's it. 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. To find out how big a paper format is, one can measure an instance with a ruler, or look up appropriate documentation. 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. following Backus' FP language with the "Def" command. Say you want to make a multiplication table for an elementary school kid near you. (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. 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. Introduction to the Tcl 3 Language The next ve chapters constitute a Tcl language tutorial. 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. Also, memory limits on modern computers are somewhere up high so only at some time in the future you might have (but maybe not want) to change to a complex database;-). Explore the Tcl exercises on Exercism Unlock more exercises as you progress. The coin values should be passed to change as a variable number of arguments which are the coin values in units (e.g., a quarter would be represented as 25) in any order. In the algebra introduced here, with a variable "a", no further simplification was so far possible. # 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}}. The correct hypot() function would be. by one the binary operators +-*/. Practical Programming in Tcl and Tk by Brent Welch, Ken Jones. Another example, cooked up by myself this time, computes the average of a list. I'm far from having digested it all, but like so often, interesting reading prompts me to do Tcl experiments, especially on weekends. #-- 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. 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." Rather, one could use read and write traces on variable M, causing it to load from, or store to, mem($HL). * Edit and save ex1proc.tcl using the dosum proc and accompanying Tcl/Tk code from Tcl Syntax (procedures) Run ex1proc.tcl. Bertrand Russell commented that the author "has revealed a new calculus, of great power and simplicity" (somehow sounds like Tcl;^). The entire syntax of Tcl is described in just 12 rules. 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. Instructions The classical introductory exercise. 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. #-- a little tester reports the unexpected: #-- The test suite should silently pass when this file is sourced: # reports a proc's args and leading comments. Creating a new syntax for a DSL would defeat the purpose of Tcl. Tcl is a powerful scripting language that runs under Unix, Linux, VMS, DOS/Windows, OS/2, and MacOS (at least). 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. Discover new exercises as you progress and get engrossed in learning new concepts and improving the way you currently write. Continuous, active development since the early 1990's. To extend Tcl, i.e. 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. Implication (if a then b, a -> b) can in expr be expressed as $a <= $b just note that the "arrow" seems to point the wrong way. In a nutshell, his FP system comprises. It is a scripting language that aims at providing the ability for applications to communicate with each other. A program without such extravaganzas is shorter and yet does the same job, so it will have been tested earlier anyway. Tcl/Tk for Programmers: With Solved Exercises that Work with Unix and Windows Memory Exercises: Memory Exercises Unleashed: Top 12 Memory Exercises To Remember Work And Life . Notice that so far we have only defined one short proc, all other operations were done with built-in Tcl commands only. Don't take this as a fundamental critique of Tcl, though its underlying model is far more simple and elegant than LISP's (what with "special forms", "reader macros"), and yet powerful enough to do just about everything possible which is sort of a mathematical thriller, if you will. with automatic analysis Like in real life, test cases have to be carefully chosen. I won't go into all details of the above code, just some: (<.,>.) 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. TCL is shell application that reads TCL command from its standard input or from a file and gives desired results. 1. 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. {AND, OR, NOT} resp. From Grade School to Raindrops. is building a list of the floor and the ceiling of its single argument, the comma being the concatenation operator here, comparable to Backus' "construction" or Joy's cleave. So here is one model of a state machine in ten lines of code. For instance, we want all books printed before 1980: We might also store our patrons in the same database (here in a different style): Without a concept of "tables", we can now introduce structures like in relational databases. 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. Let us write a simple Tcl program. 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. 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. There are over 200 exercises with solutions for both Unix and Windows platforms. and Insert is better known as fold, I suppose. 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". Here's our recommended free books that'll help you master Tcl. A filter takes one or more streams, and possibly other arguments, and reacts like a stream too. 71 coding exercises for C on Exercism. which, when called with no arguments, return 1 or 0, respectively. The idea in the paper I read is to use them as names of very simple functions: Glory be to the 11 rules of man Tcl that this is already a crude though sufficient reimplementation: The bracketed expr command is evaluated first, returning 0 or 1 as result of the comparison. 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. 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. That's all. The goto command is defined "locally", and deleted after leaving the state machine it is not meaningfully used outside of it. After version 8.0/8.0, the unusually fast development of Tcl/Tk has slowed to a more normal pace. Adding "records" to the table is as easy as. which is shorter and simpler, but meddles more directly with the stack. Newbie Tcl/Tk exercises. Exercism is fun, effective and It does so by adding the values of the hex digits: Stacks and queues are containers for data objects with typical access methods: In Tcl it is easiest to implement stacks and queues with lists, and the push method is most naturally lappend, so we only have to code a single generic line for all stacks and queues: It is pop operations in which stacks, queues, and priority queues differ: Priority (a number) has to be assigned at pushing time by pushing a list of two elements, the item itself and the priority, e.g.. Tcl/Tk 8.2.3 and Tcl/Tk 8.3.0 under windows. Different from switch, numbers are compared by numeric value, no matter whether given as decimal, octal or hex. #--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. 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. Another idea from SICP is a "smoothing" function, that averages each pair of values from the input stream. 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). 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. But for n>143 we reach the domain limit of floating point numbers. 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}. # - rewrite a proc's default arg with given value. The author (Richard Suchenwirth) declares them to be fully in the public domain. 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). This may be used for Boolean properties of numerically indexed sets of items. 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 you use the tiny testing framework explained earlier, the e.g. 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. All Exercises 122 Completed 0 In Progress 0 Available 122 Locked 0 Hello World Tutorial Exercise The classical introductory exercise. 13Solving cryptarithms 14Database experiments 14.1A simple array-based database 14.2Tables as lists of lists 15Programming Languages Laboratory 15.1GOTO: a little state machine 15.2Playing Assembler 15.3Functional programming (Backus 1977) 15.4Reusable functional components 15.5Modelling an RPN language 15.6Tacit programming 16Vector arithmetics One point that was new for me is that the distinction between operators and operands is not cast in stone. 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. But bare-bones has its advantages too: in order to see how a clockwork works, you'd better have all parts visible:). I started with Backus' first Functional Program example. But for historical reasons, the Tcl command to create a function is called proc and thus people most often call them procedures. In his Turing Award lecture, Can Programming Be Liberated from the von Neumann Style? ): proc flatten_list { l } { if { [llength $l] == 0 } { return {} } elseif { [llength $l] == 1 && [lindex $l 0] == $l } { return $l } else { set ret {} (!a || !b), but then again, these functions are equivalent. Accessing fields in a table is more fun with the field names than the numeric indexes, which is made easy by the fact that the field names are in the first row: Here is how to filter a table by giving pairs of field name and glob-style expression in addition to the header line, all rows that satisfy at least one of those come through (you can force AND behavior by just nesting such calls): This filters (and, if wanted, rearranges) columns, sort of what is called a "view": In the following few chapters you'll see how easy it is to emulate or explore other programming languages with Tcl. 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. Tcl was developed initially for Unix. 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. Procedures are just like functions we use in any other programming language such as C, Java, Python, etc. (I might have called it fun as well it sure is.) Tcl is a popular and widely used cross-platform script programming language that achieves significant productivity gains when used by skilled engineers. 122 exercises If both the operands are non-zero, then condition becomes true. Tcl Scripting Basic Examples Introducing 4th Gen Intel Xeon Scalable Processors Introducing 4th Gen Intel Xeon Scalable Processors Introducing 4th Gen Intel Xeon Scalable Processors The browser version you are using is not recommended for this site. Arguments are pushed on the stack, and the result of the "software", the stack at end, is returned. I added converters between characters and integers, and between strings and lists (see the dictionary below). Note that on infinite streams, selectors may never return, e.g. For a real 8080, one would have to say. The authors provide sample chapters available to download for free. 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. Here is a routine for querying or setting single bits in vectors, where bits are addressed by non-negative integers. 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. Tables are understood here as rectangular (matrix) arrangements of data in rows (one row per "item"/"record") and columns (one column per "field"/"element"). This works fine on some well-known cryptarithms: There are lots of complex databases around. See the examples soon to come. save it to a file for printing. 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. 2. looking for: Tcl/Tk exercises (please) 3. The pattern, is a kind of conditional in J, which could in Tcl be written. 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. Running a Tcl/Tk applet within a Tcl/Tk program. This is provided e.g. being any pre- or user-defined function). 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. 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. Tests are done with this minimal "framework": The dot product of two vectors is a scalar. Tcl - Environment Setup . On the limits: Tcl arrays may get quite large (one app was reported to store 800000 keys in Greek characters), and at some point enumerating all keys with array names db (which produces one long list) may exceed your available memory, causing the process to swap. In this article, we will know how to use procedures in TCL. For this we need to implement the construction operator, which is sort of inverse mapping while mapping a function over a sequence of inputs produces a sequence of outputs of that function applied to each input, Backus' construction maps a sequence of functions over one input to produce a sequence of results of each function to that input, e.g. all It augments the current unknown code, at the top, with a handler for. The "runtime engine" is just called "r" (not to be confused with the R language), and it boils down to a three-way switch done for each word, in eleven lines of code: Joy's rich quoting for types ([list], {set}, "string", 'char) conflict with the Tcl parser, so lists in "r" are {braced} if their length isn't 1, and (parenthesized) if it is but the word shall not be evaluated now. 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. so the two-way If is about as mighty as the real thing, give or take a few braces and redundant keywords (then, else). of Tcl. Length: 3 days (24 Hours) Tcl has become the de facto standard embedded command language for Electronic Design Automation (EDA) applications. 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. Learn and practice Tcl by completing 122 exercises that explore different concepts and ideas. 5. converting Java app to Tcl/Tk ( new thread for all the tcl/tk itcl gurus) 6. # 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. #-- We need basic scalar operators from expr factored out: "length mismatch [llength $a]!= [llength $b]". 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). (Comm. 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. 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. And three nested calls to vec are sufficient to produce the divisors list:). For creating FORTRAN and the BNF style of language description, he received the ACM Turing Award in 1977. Just like functions, procedures take arguments and return some value. 122 exercises to help you write better code. 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