on 2023年4月19日
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). 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. priority queue is any of the more clever ways: A*, Greedy, builds up a nest of foreachs suiting the problem, quick kills (with continue) to force unique values for the variables, and. Introduction to the Tcl 3 Language The next ve chapters constitute a Tcl language tutorial. 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. 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. 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. It augments the current unknown code, at the top, with a handler for. # - rewrite a proc's default arg with given value. (in a fantasy OO style): which, I admit, reads definitely better. # 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. (A && B) is false. They are however better reusable than the multable proc above. (I used uplevel instead of eval to keep all side effects in caller's scope). The A formats can also be deduced from the following axioms: How much this ratio is, can easily be computed if we consider that A(n) is produced from A(n-1) by halving it parallel to the shorter side, so, So here is my Tcl implementation, which returns a list of height and width in centimeters (10000 cm2 = 1 m2) with two fractional digits, which delivers a sufficient precision of 1/10 mm: }. For the 1000 programs with Goedel numbers 1..1000, it retains only a fraction for each stack balance: Simple starter discover the successor function (add one): Not bad: duplicate the number twice, divide by itself to get the constant 1, and add that to the original number. As everything is a string, and to Tcl "a" is {a} is a , Joy's polymorphy has to be made explicit. 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). 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. 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. 4. of Tcl. The GOTO "jumping" instruction is considered harmful in programming for many years now, but still it might be interesting to experiment with. In a frequent parlage, priority 1 is the "highest", and the number increases for "lower" priorities but you could push in an item with 0 for "ultrahigh";-) Popping a stack can be done like this: Popping a queue is similarly structured, but with so different details that I found no convenient way to factor out things: Popping a priority queue requires sorting out which item has highest priority. Example: An existence map of ZIP codes between 00000 and 99999 can be kept in a list of 3125 integers (where each element requires about 15 bytes overall), while implementing the map as an array would take 100000 * 42 bytes in worst case, but still more than a bit vector if the population isn't extremely sparse in that case, a list of 1-bit positions, retrieved with lsearch, might be more efficient in memory usage. As you see below, many functionalities can be "implemented" by just using Tcl's list functions. 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. bit foo 32 will turn foo into a list of two integers, if it was only one before. Other streams may provide a finite but very large number of elements, which would be impractical to process in one go. Of course this is no real assembler. 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. Chapters 5-8 introduce more commands and techniques and ACM 21.8, Aug. 1978, 613-641), he developed an amazing framework for functional programming, from theoretical foundations to implementation hints, e.g. 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. 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. But for n>143 we reach the domain limit of floating point numbers. 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. In Europe and elsewhere, the most widely used paper format is called A4. In addition to extensive program-ming work on Tcl, Clif offers Tcl/Tk training sessions with in-class exercises. The following script. and let's discuss it. # Here is another stream producer that returns elements from a list: # This one repeats its list endlessly, so better use it with 'more': # This is sugar for first-time assignment of static variables: # But for a simple constant stream source, just use [subst]: # more {subst 1};# will produce as many ones as you wish. TCL is string based scripting language and also a procedural language. in a priority queue, the object with the highest priority comes first. An obvious string representation of a rational is of course "n/d". An important functional form is the conditional, which at Backus looks like. Tcl casts everything into the mold of a command, even programming constructs like variable assignment and procedure definition. All Exercises 122 Completed 0 In Progress 0 Available 122 Locked 0 Hello World Tutorial Exercise The classical introductory exercise. The special item "" (the empty string) indicates that the stream is exhausted. 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.. 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. by one the binary operators +-*/. 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. 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. From Grade School to Raindrops. To find out how big a paper format is, one can measure an instance with a ruler, or look up appropriate documentation. 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). 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. Tcl 8.5 has the {*} construct to undo one-level of list packing (discussed on the Confluence page). A math book showed me the Stirling approximation to n! 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. Execution starts at the first of the states. Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. These 20 syntax will definitely help you lot to start and improve your tcl scripting a lot. 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. 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. . So, put the following source code in a test.tcl file. Instructions The classical introductory exercise. 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). The set of all defined bytecodes will be the alphabet of this little RPN language. A program without such extravaganzas is shorter and yet does the same job, so it will have been tested earlier anyway. 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 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. 7. However, as integer division takes place, it would be better to make that. 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 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. Tcl/Tk 8.2.3 and Tcl/Tk 8.3.0 under windows. The first and second arguments are the class (disregarded here, as the dash shows) and the value, the rest is up to the coder. Tcl's lists are well suited to represent sets. 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. is a popular function with super-exponential growth. I'm far from having digested it all, but like so often, interesting reading prompts me to do Tcl experiments, especially on weekends. They can be more precise than any "float" or "double" numbers on computers, as those can't exactly represent any fractions whose denominator isn't a power of 2 consider 13 which can not at any precision be exactly represented as floating-point number to base 2, nor as decimal fraction (base 10), even if bignum. true. The source code is compiled into bytecode, which is later interpreted by the Tcl interpreter. For clearer code, it is advisable to factor out frequent operations into procs, e.g. Arguments are pushed on the stack, and the result of the "software", the stack at end, is returned. The goto command is defined "locally", and deleted after leaving the state machine it is not meaningfully used outside of it. Rules in this little challenge are of the form a bcD e, where, Here's my naive implementation, which takes the tape just as the string it initially is. }, can be represented by their truth table, which for example for {$a && $b} looks like: As all but the last column just enumerate all possible combinations of the arguments, first column least-significant, the full representation of a&&b is the last column, a sequence of 0s and 1s which can be seen as binary integer, reading from bottom up: 1 0 0 0 == 8. 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? "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. Running a Tcl/Tk applet within a Tcl/Tk program. 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. 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. more is the most important "end-user" of streams, especially if they are infinite. All the rest would be there. }, Test data from http://csc.smsu.edu/~shade/333/project.txt. Like in switch, fall-through collapsing of several cases is indicated by "-", and "default" as final condition fires if none else did. 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. This idea may have been first brought up in Functional programming (Backus 1977), if not in Forth and Joy, and it's an interesting simplification compared to the lambda calculus. 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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