Car Trialling

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 AND 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"

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[bk][bk][bk][bk][bk][bk][bk]RIGHT AT "SMITH ST."[bk][bk]AND[bk][bk][bk]CAS TO 20 KMH
GO 2nd RIGHT
GO LEFT AT "SMITH STREET AND RECORD TIME
KEEP RIGHT AND THEN RECORD TIME
#

[bk][bk]1. KEEP LEFT AND THEN GO RIGHT
[bk][bk]2. CAS TO 20 KMH
[bk][bk]3. GO FIRST RIGHT AT "SMITH ST." AND CAS TO 20 KMH
[bk][bk]4. Trap!
[bk][bk]5. Trap!
[bk][bk]6. Trap!

UVA