TEXT.MAC.txt

; From the MACRO-10 ASSEMBLER PROGRAMMER'S REFERENCE MANUAL (June 1972), p. 7-9:
;
;	Example 4 (Figure 7-4) shows nested macros which use IRPC.  The desired operation
;	is to take an ASCII text string and store the characters four per word, left-justified,
;	with the character count stored in the first nine bits of the first word.
;
;	The TEXT macro counts the string characters and invokes the CODE macro to store the
;	characters four per word.  The CODE macro invokes a SHIFT macro which left-justifies the
;	last word if it is not already left-justified.  The first part of the example shows the
;	normal listing, then SALL is set to show what code the macros are generating.
;
; The original listing encoded two of the lines as follows:
;
;	IFN ZZ,<DEFINE SHIFT		;;REMAINDER LEFT
;	 IFE ZZ&777B8,>			;;IF NOT LEFT JUSTIFIED
;
; The April 1978 MACRO-10 manual says that a macro body "must be enclosed in angle brackets",
; so the DEFINE looks wrong, and the IFE contains only a closing angle bracket, which also seems
; wrong.  Perhaps what's shown above is a side-effect of some MACRO-10 listing generation bug
; and not an accurate reflection of the original code.  In any event, after making two small
; modifications below, macro10.js is able to assemble the code fine.
;
; This example also begs the question: did MACRO-10 optimize tail recursion?  Because without
; it, if the SHIFT macro required many iterations (for example, if "ZZ==ZZ_9" was replaced with
; "ZZ==ZZ+9"), wouldn't MACRO-10 blow its stack?  I've noted this in macro10.js as well.
;
	TITLE	STORE TEXT CHARACTER BY CHARACTER
	SUBTTL	%1 5-APR-72

	DEFINE TEXT (C)<
	N==0				;;INITIAL CONDITION
	IRPC C,<N==N+1>			;;COUNT CHARACTERS
	CODE (N,C)			;;CALL MACRO TO STORE TEXT
	>				;END OF TEXT MACRO

	DEFINE CODE (N,C)<
	ZZ==N				;;INITIAL CONDITION
	IRPC C,<
	IFN ZZ&777B8,<
		EXP ZZ			;;WORD FULL
		ZZ==0>			;;START AGAIN WITH 0
	ZZ==ZZ_9+"C">			;;END OF IRPC
	IFN ZZ,<DEFINE SHIFT<		;;REMAINDER LEFT
	 IFE ZZ&777B8,<			;;IF NOT LEFT JUSTIFIED
	  ZZ==ZZ_9			;;MOVE LEFT 9 BITS
	  SHIFT>			;;RECURSE
	 >				;;END OF DEFINE
	SHIFT				;;START MOVING LEFT
	EXP ZZ>				;;END OF IFN ZZ
	>				;END OF CODE MACRO

	TEXT (ABCDEFGHIJKL)
	END