From 249266232cb3ef141ca6d22d1e473fc5881a491f Mon Sep 17 00:00:00 2001
From: Paul Gardner-Stephen <paul@servalproject.org>
Date: Sun, 28 Apr 2019 21:50:52 +0930
Subject: [PATCH] begin implementing framework for interpreting BASIC
 statements.

---
 c64/basic/,aliases.s           |  5 +++++
 c64/basic/basic_execute_line.s | 11 +++++++++++
 c64/basic/basic_main_loop.s    | 29 ++++++++++++++++++++++++++---
 3 files changed, 42 insertions(+), 3 deletions(-)
 create mode 100644 c64/basic/basic_execute_line.s

diff --git a/c64/basic/,aliases.s b/c64/basic/,aliases.s
index b0b572b1..706116de 100644
--- a/c64/basic/,aliases.s
+++ b/c64/basic/,aliases.s
@@ -25,7 +25,12 @@
 	.alias basic_start_of_free_space_ptr $31
 	.alias basic_start_of_strings_ptr $33
 	.alias basic_top_of_memory_ptr $37
+	.alias basic_current_line_number $39
 	.alias basic_current_line_ptr $3d
+
+	;; Note that the statement point is in the CHRGET/CHRGOT routine
+	;; in ZP RAM.  (Compute's Mapping the 64, p25)
+	.alias basic_current_statement_ptr $7a
 	
 	.alias basic_numeric_work_area $57 ; $57 - $60 inclusive = 10 bytes
 
diff --git a/c64/basic/basic_execute_line.s b/c64/basic/basic_execute_line.s
new file mode 100644
index 00000000..12c33f00
--- /dev/null
+++ b/c64/basic/basic_execute_line.s
@@ -0,0 +1,11 @@
+	;; Go through the line until its end is reached.
+	;; If we reach the end are in direct mode, then
+	;; go back to reading input, else look for the
+	;; next line, and advance to that, or else
+	;; return to READY prompt because we have run out
+	;; of program.
+
+basic_execute_line:	
+
+
+	jmp basic_main_loop
diff --git a/c64/basic/basic_main_loop.s b/c64/basic/basic_main_loop.s
index ba1e780d..5f01837e 100644
--- a/c64/basic/basic_main_loop.s
+++ b/c64/basic/basic_main_loop.s
@@ -54,6 +54,11 @@ rsl_l1:	lda $0200,x
 	lda #$0d
 	jsr $ffd2
 
+	;; Ignore empty lines
+	lda tokenise_work1
+	beq basic_read_next_line
+
+	;; Else, tokenise the line
 	jsr tokenise_line	
 
 	;; Has the user entered a line of BASIC beginning with a number?
@@ -135,6 +140,24 @@ skip_spaces:
 	
 not_a_line:	
 
-	;;  XXX - Actually interpret the line
-	
-	jmp basic_main_loop
+	;;  Actually interpret the line
+
+	;; Setup pointer to the statement
+	lda #<$0200
+	sta basic_current_statement_ptr+0
+	lda #>$0200
+	sta basic_current_statement_ptr+1
+
+	;; There is no stored line, so zero that pointer out
+	lda #$00
+	sta basic_current_line_ptr+0
+	sta basic_current_line_ptr+1
+
+	;; Put invalid line number in current line number value,
+	;; so that we know we are in direct mode
+	;; (Compute's Mapping the 64 p19)
+	lda #$ff
+	sta basic_current_line_number+1
+
+	jmp basic_execute_line
+