): proc flatten_list { l } { if { [llength $l] == 0 } { return {} } elseif { [llength $l] == 1 && [lindex $l 0] == $l } { return $l } else { set ret {} 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). In Tcl, a sensible implementation for compact data storage would be as a list of lists. 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. The cute name "e.g." 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:). 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. In both cond and body you may use the variable args that holds the problem command unknown was invoked with. 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". (One might truncate the list at front if it gets too long). Just say "Hello, World!". Tcl/Tk for Programmers is an introduction to the high-level Tcl/Tk scripting language for experienced programmers with either Unix or Windows background. The source files for Tcl programs are named with the extension ".tcl". Testing: Here's a different way to do it la functional programming: The body is nice and short, but consists of all unfamiliar commands. 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. #-- 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:). Discussion: With the above code, it was possible to reproduce quite some behavior of streams as documented in SICP, not as data structures but with Tcl procs (though procs are data too, in some sense). Our mentors will help you learn to think like a Tcl developer and how to write idiomatic code in Tcl. #-- 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. OO (Object Orientation) is a style in programming languages popular since Smalltalk, and especially C++, Java, etc. Conversely, postulating non-equivalence turns out to be false in all cases, hence a contradiction: So again, we have a little proving engine, and simpler than last time. Assume variable A holds 1 and variable B holds 0, then . 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. 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. Grade School Given students' names along with the grade that they are in, create a roster for the school. Let us write a simple Tcl program. Adding a book to the database can be simply done by, Note that, as we never specified what fields a record shall contain, we can add whatever we see fit. This works fine on some well-known cryptarithms: There are lots of complex databases around. 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. This page is not available in other languages. # Multiple documentation lines are allowed. Though slick at first sight, we actually have to type more. For example, in. 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. 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. Another idea from SICP is a "smoothing" function, that averages each pair of values from the input stream. One point that was new for me is that the distinction between operators and operands is not cast in stone. For such few values it is most efficient to just look them up in a pre-built table, as Tcllib's math::factorial does. Compared to an RPN language, hypot would be. following Backus' FP language with the "Def" command. in a priority queue, the object with the highest priority comes first. Introduction to the Tcl 3 Language The next ve chapters constitute a Tcl language tutorial. and the experimental alpha version 8.1/8.1. Chapters 5-8 introduce more commands and techniques and Tcl - Logical Operators. Exercise 1 - Tcl procedure. First published January 1, 1998. 100% free. Write a function to determine if a list is a sublist of another list. In fact, the float limit is at n>170, so an intermediate result in the Stirling formula must have busted at 144. (I used uplevel instead of eval to keep all side effects in caller's scope). Here's typical set operations. The Tcl track on Exercism has 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. 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 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. This may be used for Boolean properties of numerically indexed sets of items. 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. If any of the two operands is non-zero, then . Elements are not removed by the popping, but (if necessary) when re-pushing. 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. execution of the script "++" should sum its three arguments (1+(2+3)), and return 6. It aims at providing ability for programs to interact with other programs and also for acting as an embeddable interpreter. 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. This video covers the basics that you need to start writing scripts with Tool Command Language (TCL or Tickle).Following topics are explained with simple exa. Tcl/Tk for Programmers is an introduction to the high-level Tcl/Tk scripting language for experienced programmers with either Unix or Windows background. 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). Following table shows all the logical operators supported by Tcl language. A further optimization could be to tally value strings, and replace the frequent ones with "@$id", where db(@$id) holds the value once, and only db'get has to be adapted to redirect the query. of Tcl. The ebook version (PDF format) is available from Gumroad .. lines make the self-test; otherwise they just illustrate how the operations should work. bit foo 32 will turn foo into a list of two integers, if it was only one before. In a nutshell, his FP system comprises. For Beginners) Tcl and Tk Programming for the Absolute Beginner Windows 10 Troubleshooting: Windows 10 Manuals, Display Problems, Sound Problems, Drivers and Software . The following code was created in the Tcl chatroom, instigated by the quote: "A computer is a state machine. The following scripts are plain Tcl, they don't use the Tk GUI toolkit (there's a separate chapter for those). For Tcl, there have been several OO extensions/frameworks (incr Tcl, XOTcl, stooop, Snit to name a few) in different flavors, but none can be considered as standard followed by a majority of users. #-- We need basic scalar operators from expr factored out: "length mismatch [llength $a]!= [llength $b]". Continuous, active development since the early 1990's. Of course, with growing databases we may reach memory limits: arrays need some extra storage for administration. 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 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. But for historical reasons, the Tcl command to create a function is called proc and thus people most often call them procedures. input, sorts it, and acts as a stream source on the output: Now for the example in SICP: find the second prime in the interval between 10000 and 1000000. {AND, OR, NOT} resp. 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. All Tcl files will have an extension, i.e., .tcl. In Tcl, the two ways of reading a file are a good example: The second construct may be less efficient, but is robust for gigabyte-sized files. for installation, user privileges, and system self-protection. Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. That's easily had too, given a sum function: Here's a little application for this: a vector factorizer, that produces the list of divisors for a given integer. Tests are done with this minimal "framework": The dot product of two vectors is a scalar. Tcl is a general purpose multi-paradigm system programming language. 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. Arguments are pushed on the stack, and the result of the "software", the stack at end, is returned. The special item "" (the empty string) indicates that the stream is exhausted. Threads are for people who can't program state machines.". The code below also serves as usage example: }. Procedures are just like functions we use in any other programming language such as C, Java, Python, etc. It was then ported to Windows, DOS, OS/2, and Mac OSX. If you are able to automate below few task, more then 50% of work (based on TCL) can be done easily. Rules are also taken as strings, whose parts can easily be extracted with string index as it's used so often here, I alias it to @. 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. # This filter collects its input (should be finite;-) into a list: # $ streamlist {foo bar grill a} | sort | collect => a bar foo grill. ", 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). This makes sense, even in Tcl, where one might implement them as. The extending code what is prepended to the previous unknown body. 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. Live Demo #!/usr/bin/tclsh puts "Hello, World!" Assuming, Tcl environment is setup correctly; let's run the program after switching to file's directory and then execute the program using $ tclsh test.tcl 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. 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 the algebra introduced here, with a variable "a", no further simplification was so far possible. 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. 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. 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. 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. And three nested calls to vec are sufficient to produce the divisors list:). giving the correct result 2.5. Single bytecodes are executed, only to measure their effect on the stack. 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. Every language has its own way of doing things. was instigated by the fact that in J, "NB." So let's get the pieces together. A Functional Style and Its Algebra of Programs. As we've seen that
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