I would bet people have been waiting for this one for a LOOOOONG time. (What do you mean, the challenge is over and nobody cares any more?)
Behold... I here present a solution in
Befunge-93!
It weighs in at a whopping 973 charaters (or 688 if you are charitable enough to ignore whitespace, which is only used for formatting and does nothing in actual code).
Caveat: I wrote my own Befunge-93 interpreter in Perl a short while ago, and unfortunately this is all I've really had time with which to test it. I'm reasonably confident in its correctness in general, but it might have an odd limitation with regard to EOF: Since Perl's <> operator returns undef at the end of file, this is processed as a 0 in the numeric context. For C-based implementations where EOF has a different value (-1 say), this code might not work.
003pv >~v> #v_"a"43g-!#v_23g03p33v>v
>39#<*v :: >:52*-!v >"rorrE",vg2*
######1 >^vp31+1g31$_03g13gp vv,,<15,
a#3 >0v vp30+1g30<>,,#3^@
######p $ 0vg34"a"< > >vp
^ > ^ p3<>-#v_:05g-!|>:15g-!| $
> v^ < < < >^v-g52:< $
v _ >52*"eslaf",,vv|-g53:_ v
: ^-"#">#:< #@,,,,<<>:43p0 v0 p34<
>">"-!vgv< ^0p33g31p32-1g3<
^ <#g1|-g34_v#-g34_v#-g34">13g1v>03g1-v>03g1+03p$v $$
>^ _#-v 1>g1-1v>+13pv >03p v pp
^_:"^"^#|^g30 <3# $< $<>^33
^!-"<":<>"v"v^># p#$<> $^44
^ >#^#_ :" "-#v_ ^ > ^gg
v g34$< ^!$3p$^>05g43p$ ^55
>,@ |!-"\" :_$43g:">"-!|> ^$32
*v"x":< >-^ ^4g52<>:"^" -#v_^
5>-!#v_"ror"vv$p34g51:<>#| !-"<":<#|
^2,,, ,,"er"<>v #^^#<>05g43p$$^>^
>52*"eurt",,,,,@>15g4 3p$$$$ ^#
>:"v"\:"<"\: "^" -!#^_-!#^_-! ^
> ^
Explanation
If you're not familiar with the Befunge syntax and operation, check here.
Befunge is a stack-based language, but there are commands that allow one to write characters to the Befunge code. I take advantage of that in two places. First, I copy the entire input onto the Befunge board, but located a couple of lines below the actual written code. (Of course, this is never actually visible when the code runs.)
The other place is near the the upper-left:
######
a#
######
In this case, the area I've highlighted above is where I store a couple of coordinates. The first column in the middle row there is where I store the x-coordinate for the current "cursor position"; the second column is where I store the y-coordinate; the next two columns are for storing the x- and y-coordinate of the laser beam source when that is found; and the final column (with the 'a' character in it) is eventually overwritten to contain the current beam direction, which obviously changes as the beam's path is traced.
The program starts by placing (0,27) as the initial cursor position. Then input is read one character at a time and placed in the cursor position; newlines merely cause the y-coordinate to increase and the x-coordinate to go back to 0, just like a real carriage return. Eventually undef is read by the interpreter and that 0 character value is used to signal the end of input and move on to the laser iteration steps. When the laser character [<>^v] is read, that is also copied to the memory repository (over the 'a' character) and its coordinates are copied to the columns just to the left.
The end result of all of this is that the entire file is basically copied into the Befunge code, a little ways below the actual code traversed.
Afterwards, the beam location is copied back into the cursor locations, and the following iteration is performed:
- Check for the current beam direction and increment or decrement the cursor coordinates appropriately. (I do this first to avoid having to deal with the corner case of the laser beam right on the first move.)
- Read the character at that location.
- If the character is "#", put newline and "false" on the stack, print, and end.
- Compare it to all of the beam characters [<>^v]; if there's a match, also print "false\n" and end.
- If the character is a space, empty the stack and continue.
- If the character is a forward slash, get the beam direction onto the stack and compare it to each of the direction characters in turn. When one is found, the new direction is stored at that same spot in the code and the loop repeats.
- If the character is a backslash, do basically the same thing as the above (except with the proper mapping for backslash).
- If the character is 'x', we've hit the target. Print "true\n" and exit.
- If the character is none of these, print "error\n" and exit.
If there's enough demand for it, I'll try to point out exactly where in the code all this is accomplished.
