todo

由一个古老的BASIC解释器改进而成, 保留了ANSI C固有的艺术美感.

	- POPEN blocks in windows in interactive mode, needs correction.

I don't know why. Someone knows a good implementation of popen on Win32?

	- There is no correct implementation of TAB yet, except in graphics
mode. In the meantime we simply write a number of spaces corresponding to
the parameter of TAB.

	- INPUT and LINE INPUT not work yet in graphisc mode.