Some letterboxes however remain "word of mouth" and the clues to their location can only be obtained from the person who placed the box. Clues to the locations of letterboxes are published by the "100 Club" in an annual catalogue. Membership of the "100 Club" is open to anyone who has found at least 100 letterboxes on Dartmoor. As a result, the tradition of leaving a letter or postcard in the box has been forgotten. Increasingly, however, letterboxes have been located in relatively accessible sites and today there are thousands of letterboxes, many within easy walking distance of the road. Until the 1970s there were no more than a dozen such sites around the moor, usually in the most inaccessible locations. The first Dartmoor letterboxes were so remote and well-hidden that only the most determined walkers would find them, allowing weeks to pass before the letter made its way home. In 1938 a plaque and letterbox in Crossing's memory were placed at Duck's Pool on southern Dartmoor. The next person to discover the site would collect the postcards and post them. From this hikers on the moors began to leave a letter or postcard inside a box along the trail (sometimes addressed to themselves, sometimes a friend or relative)-hence the name "letterboxing". William Crossing in his Guide to Dartmoor states that a well known Dartmoor guide (James Perrott ) placed a bottle for visiting cards at Cranmere Pool on the northern moor in 1854. This program asks the user for their name, greets them, then asks their age, and responds differently whether the user is 20 or more years old.The origin of letterboxing can be traced to Dartmoor, Devon, England in 1854. LcMAaab Pa ! This program should print out 2. This program increments a twice and prints the result. Hello World ! This program prints "Hello world" Anything that comes after a ! character on a single line is ignored by the interpreter. Each line of input will have its own line of output, so place your line breaks carefully.Ĭomments can also be placed in programs. If the string contains underscores, they will be printed as spaces.Ī valid Letterbox program is a series of function calls separated by spaces and/or line breaks. In lieu of this, Letterbox treats underscores (_) in strings as spaces. NOTE: No spaces are allowed in strings, because whitespace is not allowed within function calls. A string manipulator function has the form A:string where A is the function name, and everything after the colon (:) is the string you wish to pass in. Otherwise, does nothing.įor ease of I/O, Letterbox has some (albeit limited) string shortcuts. If a is true (nonzero), executes function F. Repeatedly executes function F, repeating a times. is another function call, which can have its own arguments after it. where A is the function name, b is a variable argument, and F. Prefix functions are functions that take in other functions as arguments. Pauses execution, gets input from the user of a certain type, and stores the value in a Operations: equal to, and, or, xor (exclusive or) This result will always be 0 (false) or 1 (true). Performs a boolean operation on b and c and stores the result in a. Operations: add, subtract, multiply, divide, equal to, greater than, less than Performs a mathematical operation on b and c and stores the result in a. are the variable arguments of the function. These take the form AXb., where A is the function name, X is a key letter that specifies what operation the function will perform, and b. Since there are only 26 possible simple function names in Letterbox, some functions have been combined into one in order to save letters for other functions that might possibly be implemented in the future. Using uppercase A as an argument resets all variables.īoolean negation. Variables are considered "true" if their value is nonzero, and "false" if their value is zero.įollowing are the four types of Letterbox function formats:Ī simple function follows the format Ab., where A is the function name and b. All Letterbox function names are singular uppercase English letters. No whitespace is allowed between these characters, as spaces are what separate Letterbox statements. A is the name of the function we are calling while b and c are two variables we are passing in as arguments. They can also technically hold strings (as the language is built over Python) but this implementation is buggy at best.Ī Letterbox function call generally looks like Abc. Each variable can hold a single number, which can be an integer or a decimal, positive or negative. Letterbox is case-sensitive, and uppercase letters are not variable names. Each is labeled as a lowercase letter from a to z and each is set to 0 by default. registers, for those familiar with Assembly). Letterbox programs manipulate a bank of 26 variables (a.k.a.
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