In-Depth Coverage of the Icon Programming Language
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چکیده
Here's the challenge: Model string synthesis with the mapping expr1 ? expr2 → Eform(Bform(expr1),expr2) and provide appropriate procedures for Bform() and Eform(). Use the global variables subject, s_pos, object, and o_pos for the state variables. (Do not use &subject and &pos.) In addition, provide the following analysis and synthesis procedures: • smove(i) and stab(i), which are the same as move(i) and tab(i) in string scanning. • omove(i) and otab(i), which are the same as smove(i) and stab(i), except they apply to the object, not the subject. • oplace(s), which inserts s in the object following the current position in it, changes the position to the end of the inserted string, and returns the new value of the position. • xswap(), which swaps the values of the subject and the object, and sets both positions to 1. • odelete(i), which deletes the i characters of the object following the current position. It does not change the position, but returns it as value. • spos(i), which is the same as pos(i) for string scanning. • opos(i), which is the same as spos(i), but for the object, instead of the subject. Here's an example of the use of these procedures: write("abcde" ? { while smove(1) do oplace(smove(1)) oplace("]") otab(1) oplace("[") }) The value written is [bd]. Take this as an exercise and see what you can do with it. Don't hesitate to try to improve on the procedures suggested here. We'll give our solution to this exercise in the next issue of the Analyst.
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