LD	A,E	The 'last' operation code.
		AND	+3F	Strip off bits 6 and 7 to convert
		LD	B,A	the operation code to a
				calculator offset.
		RST	0028,FP-CALC	Now use the calculator.
		DEFB	+3B,fp-calc-2	Perform the actual operation
		DEFB	+38,end-calc	It has been done.
		JR	2764,S-RUNTEST	Jump forward.

An important part of syntax checking involves the testing of the operation to ensure that the nature of the 'last value' is of the correct type for the operation under consideration.

275B	S-SYNTEST	LD	A,E	Get the 'last' operation code.
		XOR	(FLAGS)	This tests the nature of the 'last
		AND	+40	value' against the requirement
				of the operation. They are to be
				the same for correct syntax.
2761	S-RPORT-C	JP	NZ,1C8A,REPORT-C	Jump if syntax fails.

Before jumping back to go round the loop again the nature of the 'last value' must be recorded in FLAGS.

2764	S-RUNTEST	POP	DE	Get the 'last' operation code.
		LD	HL,+5C3B	This is FLAGS.
		SET	6,(HL)	Assume result to be numeric.
		BIT	7,E	Jump forward if the nature of
		JR	NZ,2770,S-LOOPEND	'last value' is numeric.
		RES	6,(HL)	It is string.
2770	S-LOOPEND	POP	BC	Get the 'present' values into BC:
		JR	2734,S-LOOP	Jump back.

Whenever the 'present' operation binds tighter, the 'last' and the 'present' values go back on the machine stack. However if the 'present' operation requires a string as its operand then the operation code is modified to indicate this requirement.

2773	S-TIGHTER	PUSH	DE	The 'last' values go on the stack.
		LD	A,C	Get the 'present' operation
				code.
		BIT	6,(FLAGS)	Do not modify the operation
		JR	NZ,2790,S-NEXT	code if dealing with a numeric
				operand.
		AND	+3F	Clear bits 6 and 7.
		ADD	A,+08	Increase the code by +08 hex.
		LD	C,A	Return the code to the C
				register.
		CP	+10	Is the operation 'AND'?
		JR	NZ,2788,S-NOT-AND	Jump if it is not so.
		SET	6,C	'AND' requires a numeric
				operand.
		JR	2790,S-NEXT	Jump forward.
2788	S-NOT-AND	JR	C,2761,S-RPORT-C	The operations -,*,/,^ and OR
				are not possible between strings.
		CP	+17	Is the operation a '+'?
		JR	Z,2790,S-NEXT	Jump if it is so.
		SET	7,C	The other operations yield a
				numeric result.
2790	S-NEXT	PUSH	BC	The 'present' values go on the
				machine stack.
		RST	0020,NEXT-CHAR	Consider the next character.
		JP	24FF,S-LOOP-1	Go around the loop again.