link hexcvt

procedure main()
ue := "http%3A%2F%2Ffoo%20bar%2F"
ud := decodeURL(ue) | stop("Improperly encoded string ",image(ue))
write("encoded = ",image(ue))
write("decoded = ",image(ue))
end

procedure decodeURL(s)              #: decode URL/URI encoded data
static de
initial {                           # build lookup table for everything
  de := table()
  every de[hexstring(ord(c := !string(&ascii)),2)] := c
  }

c := ""
s ? until pos(0) do                 # decode every %xx or fail
   c ||:= if ="%" then \de[move(2)] | fail
   else move(1)
return c
end