12basic ]=[ interpreter

CODE$=INPUT$()
STRICT=TRUE
STACK#=[]
CALLSTACK#=[]
I:NUMBER=0
CHAR$:STRING
DO
	NEXTCHAR()
	SWITCH CHAR$
		CASE "["
			VALUE=0
			SIGN=1
			DO
				NEXTCHAR()
				SWITCH CHAR$
					CASE "]"
						IF !DONOTHING THEN STACK#.PUSH(VALUE*SIGN)
						BREAK
					CASE "["
						IF VALUE==0 THEN SIGN=-1
						VALUE=VALUE*10
					CASE "="
						VALUE=VALUE+1
					CASE ""
						PRINT "ERROR: UNTERMINATED NUMBER LITERAL"
						IF STRICT THEN STOP
				ENDSWITCH
			LOOP
		CASE "="
			START=I-1
			OPERATION$=""
			DO
				NEXTCHAR()
				SWITCH CHAR$
					CASE "="
						SWITCH OPERATION$
							CASE "" 'end loop
								IF DONOTHING THEN
									LEVEL=LEVEL-1
									IF LEVEL==0 THEN
										DONOTHING=FALSE
									ENDIF
								ELSE
									IF CALLSTACK#.LENGTH() THEN
										I=CALLSTACK#.POP()
									ELSE
										I=0
									ENDIF
								ENDIF
							CASE "]" 'loop
								IF DONOTHING THEN
									LEVEL=LEVEL+1
								ELSE
									CALLSTACK#.PUSH(START)
								ENDIF
							CASE "[" 'while
								IF DONOTHING THEN
									LEVEL=LEVEL+1
								ELSE
									IF STACK#.GET(STACK#.LENGTH()-1) THEN
										CALLSTACK#.PUSH(START)
									ELSE
										DONOTHING=TRUE
										LEVEL=1
									ENDIF
								ENDIF
							CASE "][" 'function def
								IF DONOTHING THEN
									LEVEL=LEVEL+1
								ELSE
									STACK#.PUSH(I)
									DONOTHING=TRUE
									LEVEL=1
								ENDIF
							CASE "[]" 'function call
								IF !DONOTHING THEN
									CALLSTACK#.PUSH(I)
									I=POPSTACK()
								ENDIF
							ELSE
								PRINT "ERROR: UNDEFINED LOOP ",OPERATION$
								IF STRICT THEN STOP
						ENDSWITCH
						BREAK
					CASE "]"
						OPERATION$=OPERATION$+"]"
					CASE "["
						OPERATION$=OPERATION$+"["
					CASE ""
						PRINT "ERROR: UNTERMINATED LOOP OPERATOR"
						IF STRICT THEN STOP
				ENDSWITCH
			LOOP
		CASE "]"
			OPERATION$=""
			DO
				NEXTCHAR()
				SWITCH CHAR$
					CASE "["
						IF !DONOTHING THEN
							SWITCH OPERATION$
								CASE ""
									PRINT POPSTACK()
								CASE "="
									OUTPUT(POPSTACK().CHR$())
								CASE "]" 'input number 'dup
									A=POPSTACK()
									STACK#.PUSH(A)
									STACK#.PUSH(A)
								CASE "==" 'compare
									A=POPSTACK()
									B=POPSTACK()
									STACK#.PUSH(A==B) 'maybe do sign subtract?
								CASE "=]" 'add
									A=POPSTACK()
									B=POPSTACK()
									STACK#.PUSH(A+B)
								CASE "]=" 'subtract
									A=POPSTACK()
									B=POPSTACK()
									STACK#.PUSH(A-B)
								CASE "]]"

								CASE "==]" 'input char

								CASE "=]]" 'input num

								ELSE
									PRINT "ERROR: UNDEFINED OPERATION",OPERATION$
									IF STRICT THEN STOP
							ENDSWITCH
						ENDIF
						BREAK
					CASE "]"
						OPERATION$=OPERATION$+"]"
					CASE "="
						OPERATION$=OPERATION$+"="
					CASE ""
						PRINT "ERROR: UNTERMINATED OPERATOR"
						IF STRICT THEN STOP
				ENDSWITCH
			LOOP
		CASE ""
			BREAK
	ENDSWITCH
LOOP
FUNC NEXTCHAR
	CHAR$=CODE$.MID$(I)I=I+1
ENDFUNC
FUNC POPSTACK
	IF STACK#.LENGTH() THEN RETURN STACK#.POP()
	RETURN 0
ENDFUNC