// befunge-93

X:"\\"									/ escape
Q:"\""									/ quote
N:"0123456789"								/ numeric

p:{[n;x](-n)#(&n),x}							/ left overtake, pad with 0
x:{[n;f]{v .(((-n)_ x),,f . p[n]x;y)}}					/ nary apply, append 1
y:{[n;f]{v .(((-n)_ x),f . p[n]x;y)}}					/ nary apply, append k
z:{[d]{v .(x;@[y;1;:;d[]])}}						/ modify direction
w:{[d]{v .(-1_ x;@[y;1;:;d@~*p[1]x])}}					/ modify direction conditional
v:{(x;@[y;2;:;(+/y 1 2)!'^*y])}						/ vector
B::"";b:{[f]if[~#B;B::0:`];r:f B;B::(#r)_ B;r}				/ input buffer

O:+(("+"	;x[2;+])						/ add
    ("-"	;x[2;-])						/ sub
    ("*"	;x[2;*])						/ mul
    ("/"	;x[2;_%])						/ div
    ("%"	;x[2;!])						/ mod
    ("!"	;x[1;~:])						/ not
    ("`"	;x[2;>])						/ more
    (">"	;z[0 1])						/ right
    ("<"	;z[0 -1])						/ left
    ("v"	;z[ 1 0])						/ down
    ("^"	;z[-1 0])						/ up
    ("?"	;z[(0 1;0 -1;1 0;-1 0)()_draw 4])			/ randomize direction
    ("_"	;w[(0 -1;0 1)])						/ if true left else right
    ("|"	;w[(-1 0;1 0)])						/ if true up else down
    (Q		;{v .(x;@[y;3;:;1])})					/ enter quote mode
    (":"	;y[1;{(x;x)}])						/ dup
    (X		;y[2;{(y;x)}])						/ swap
    ("$"	;y[1;{()}])						/ pop
    ("."	;y[1;{`0:,$x;()}])					/ pop val -> output			
    (","	;y[1;{`0:_ci x;()}])					/ pop val -> char -> output
    ("#"	;{2(v .)/(x;y)})					/ bridge (skip)
    ("g"	;{v .((-2_ x),_ic y[0].|p[2;x];y)})			/ get
    ("p"	;{v .(-3_ x;.[y;0,|p[2;x];:;_ci p[3;x]0])})		/ put
    ("&"	;{v .(x,0$b{(x?" ")#x};y)})				/ input -> val
    ("~"	;{v . (x,_ic b(*:);y)})					/ input -> char
    ("@"	;{(x;y)}))						/ stop

/ x = stack
/ y = (program;y-dir,x-dir;y,x;quote-mode)

/ apply - in normal mode:

a:{t:y[0]. y 2;:[y 3;q;t _in N;{v .(x,0$y;z)};t _in*O;{O[1;O[0]?y][x;z]};{v .(x;z)}][x;t;y]}

/ apply - in quote mode:

q:{v .:[y=X;(.[x;();,;_ic y];@[z;3;:;-1]);(1=z 3)&y=Q;(x;@[z;3;:;0]);(.[x;();,;_ic y];@[z;3;:;1])]}

/ gui engine:

f:{m n F:::[@x;"";"."_in x;x;x,".bf"]}					/ file
m:{(();({x,y#" "}'[x;80-#:'x:25#x,25#,""];0 1;0 0;0))}			/ normalize to 25 80
n:{:[#x;0:x;,""]}							/ file read
r:{P::x;W.P::,:''+P[1;0];`show$`.k.W;}					/ evaluate
k:{P::a . P;s[]}							/ step
i:{P::(a .)/P;s[]}							/ run
s:{W.P::,:''+P[1;0];W[`D`C`Q]:P[1;1 2 3];W.S::5:*P}			/ single
j:{.t..t::[W.J;".k.k[]"];."\\t ",$W.J*.001}				/ timer
l:{(5:y),":",("<>^v"(0 -1;0 1;-1 0;1 0)?x),":",$z}			/ label

/ gui display:

W.P:80 25#,," "								/ program window
W.P..bg:{:[_i~|P[1;2];999900;999999]}					/ yellow cell is current pointer
W.P..e..d:".k.W.E"							/ edit toggle
W.P..l..d:".k.F"							/ befunge program running
W.P..t:"if[#_i;.[`.k.P;1 0,|_i;:;*_v ._i]]"				/ update program
W.P..kr:".k.P[1;2]:|_i;.k.W.P::"					/ set pointer here
W.S:"";W.S..e:0;W.S..f:-100$;W.S..l:""					/ stack
W.K:".k.k[]";W.K..c:`button;W.K..x:8;W.K..l..d:".k.l ..k.P[1;1 2 3]"	/ one instruction
W.J:0;W.J..c:`check;W.J..l:`Step;W.J..t:".k.j[]"			/ step program
W.I:0;W.I..c:`check;W.I..l:`Run;W.I..t:".k.i[]"				/ run program
W.E:0;W.E..c:`check;W.E..l:`Edit					/ edit program
W..a:(`P;`K`J`I`E`S);W..c:`form;W..l:"Befunge-93";W..y:29;W..x:100	/ window attributes

/ start:

r f@*_i									/ start on file _i 0