work towards being able to delete BASIC lines

c64/basic/basic_delete_line.s

@@ -5,5 +5,56 @@
 	;; banked out. Oh, yes, and we have to update all the links in
 	;; the following basic lines.
 basic_delete_line:
+
+	jsr printf
+	.byte "DELETING LINE AT $"
+	.byte $f1,<basic_current_line_ptr,>basic_current_line_ptr
+	.byte $f0,<basic_current_line_ptr,>basic_current_line_ptr
+	.byte $0d,0
+
+	;; Get address of next line
+	ldx #<basic_current_line_ptr
+	ldy #0
+	jsr peek_under_roms
+	sta tokenise_work3
+	iny
+	jsr peek_under_roms
+	sta tokenise_work4
+
+	;; Work out length of this line by looking at the pointer
+	lda tokenise_work3
 	sec
+	sbc basic_current_line_ptr+0
+	sta tokenise_work3
+	lda tokenise_work4
+	sbc #0
+	cmp #$00
+	beq +
+	;; Line length is <0 or >255 bytes.
+	;; Either way, things are bad, so abort.
+	ldx #35
+	jmp do_basic_error
+*
+	;; Length can now be safely assumed to be in the low
+	;; byte only, i.e., stored in tokenise_work3
+
+	lda tokenise_work3
+	pha
+	tax
+
+	;; Shuffle everything down
+	jsr basic_shift_mem_down_and_relink
+
+	;; Now decrease top of BASIC mem
+	pla
+	sta tokenise_work3
+	lda basic_end_of_text_ptr+0
+	sec
+	sbc tokenise_work3
+	sta basic_end_of_text_ptr+0
+	lda basic_end_of_text_ptr+1
+	sbc #0
+	sta basic_end_of_text_ptr+1
+
+	clc
 	rts