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Car trialling requires the following of carefully worded instructions. When setting a trial, the organiser places traps in the instructions to catch out the unwary.
Write a program to determine whether an instruction obeys the following rules, which are loosely based on real car trialling instructions. BOLD-TEXT indicates text as it appears in the instruction (case sensitive), | separates options of which exactly one must be chosen, and .. expands, so A..D is equivalent to A|B|C|D.
instruction = navigational | time-keeping | navigational b time-keeping navigational = directional | navigational AND THEN directional directional = how direction | how direction where how = GO | GO when | KEEP direction = RIGHT | LEFT when = FIRST | SECOND | THIRD where = AT sign sign =
"signwords = s-word | signwords s-word s-word = letter | s-word letter letter = A..Z | . time-keeping = record | change record = RECORD TIME change = cas TO nnn KMH cas = CHANGE AVERAGE SPEED | CAS nnn = digit | nnn digit digit = 0..9
Note that s-word and nnn are sequences of letters and digits respectively, with no intervening spaces. There will be one or more spaces between items except before a period (.), after the opening speech marks or before the closing speech marks.
Each input line will consist of not more than 75 characters. The input will be terminated by a line consisting of a single #.
The output will consist of a series of sequentially numbered lines, either containing the valid instruction, or the text
Trap! if the line did not obey the rules. The line number will be right justified in a field of 3 characters, followed by a full-stop, a single space, and the instruction, with sequences of more than one space reduced to single spaces.
KEEP LEFT AND THEN GO RIGHT CAS TO 20 KMH GO FIRST RIGHT AT "SMITH ST." AND CAS TO 20 KMH GO 2nd RIGHT GO LEFT AT "SMITH STREET AND RECORD TIME KEEP RIGHT AND THEN RECORD TIME #
1. KEEP LEFT AND THEN GO RIGHT 2. CAS TO 20 KMH 3. GO FIRST RIGHT AT "SMITH ST." AND CAS TO 20 KMH 4. Trap! 5. Trap! 6. Trap!