From 421b56b401697dda99a7cfe402f16943ea094cd6 Mon Sep 17 00:00:00 2001
From: Ralph Ronnquist <ralph.ronnquist@gmail.com>
Date: Fri, 4 Jun 2021 18:27:33 +1000
Subject: [PATCH] adding the AGAIN control word

---
 adoc/p_again.adoc | 16 ++++++++++++++++
 control.asm       | 21 ++++++++++++++++++++-
 reference.adoc    |  2 ++
 wordindex.adoc    |  1 +
 4 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 adoc/p_again.adoc

diff --git a/adoc/p_again.adoc b/adoc/p_again.adoc
new file mode 100644
index 0000000..62e72f1
--- /dev/null
+++ b/adoc/p_again.adoc
@@ -0,0 +1,16 @@
+// control.asm:	WORD p_again,'AGAIN',fasm
+
+anchor:p_again[]
+
+=== Word: AGAIN
+
+....
+Data stack: Compiling: ( -- a )
+....
+
+"AGAIN" is an immediate function word that is used together with
+<<p_begin,BEGIN>> and instead of <<p_end,END>> to implement structured
+execution control. AGAIN scans the datastack for the nearest preceding
+BEGIN marker and lays out an unconditional branch from this point the
+beginning of the block during execution. It thereafter performs the
+<<p_end,END>> compile action to end the block.
diff --git a/control.asm b/control.asm
index b6bfe0f..949f48c 100644
--- a/control.asm
+++ b/control.asm
@@ -165,4 +165,23 @@ p_end_ending:
 	pop rbx
 	next
 
-	
+	WORD p_again,'AGAIN',fasm,IMMEDIATE
+	;; Compiling: ( a 0 * -- )
+	;; Lay out unconditional loop-back, then perform END action
+	mov rax,qword [p_here_DFA]
+	mov qword [rax],p_branch_CFA
+	mov qword [rax+8],0
+	add rax,16
+	mov qword [p_here_DFA],rax
+	mov rbx,rsp
+p_again_loop:
+	cmp qword [rbx],0
+	je p_ifagain_resolve
+	add rbx,8
+	jmp p_ifagain_loop
+p_again_resolve:
+	mov rbx,qword [rbx+8]
+	sub rbx,rax
+	mov qword [rax-8],rbx
+	mov rax,rsp
+	jmp p_end_scan
diff --git a/reference.adoc b/reference.adoc
index 1700ddf..7bf6815 100644
--- a/reference.adoc
+++ b/reference.adoc
@@ -41,6 +41,8 @@ include::adoc/p_Rgt.adoc[]
 include::separator.adoc[]
 include::adoc/p_abs.adoc[]
 include::separator.adoc[]
+include::adoc/p_again.adoc[]
+include::separator.adoc[]
 include::adoc/p_allot.adoc[]
 include::separator.adoc[]
 include::adoc/p_and.adoc[]
diff --git a/wordindex.adoc b/wordindex.adoc
index ebac853..2ffe08e 100644
--- a/wordindex.adoc
+++ b/wordindex.adoc
@@ -58,6 +58,7 @@ xref:p_2over[2OVER] {nbsp}
 xref:p_2swap[2SWAP] {nbsp}
 
 xref:p_abs[ABS] {nbsp}
+xref:p_again[AGAIN] {nbsp}
 xref:p_allot[ALLOT] {nbsp}
 xref:p_and[AND] {nbsp}
 <<inline_code,[ASM]>> {nbsp}
-- 
2.39.2