From 2338bd8a98d87b5f2449943b35e381499a1efb45 Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Thu, 3 Sep 2020 19:58:47 +0200
Subject: [PATCH] implemented 'IF' BASIC command

---
 src/basic/basic_commands/cmd__unimplemented.s |  2 --
 src/basic/basic_commands/cmd_if.s             | 29 +++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 src/basic/basic_commands/cmd_if.s

diff --git a/src/basic/basic_commands/cmd__unimplemented.s b/src/basic/basic_commands/cmd__unimplemented.s
index dc96a1c2..9b76d5f6 100644
--- a/src/basic/basic_commands/cmd__unimplemented.s
+++ b/src/basic/basic_commands/cmd__unimplemented.s
@@ -21,8 +21,6 @@ cmd_input:
 	nop
 cmd_read:
 	nop
-cmd_if:
-	nop
 cmd_gosub:
 	nop
 cmd_return:
diff --git a/src/basic/basic_commands/cmd_if.s b/src/basic/basic_commands/cmd_if.s
new file mode 100644
index 00000000..1c52ad63
--- /dev/null
+++ b/src/basic/basic_commands/cmd_if.s
@@ -0,0 +1,29 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+cmd_if:
+
+	// Calculate expression
+
+	jsr FRMEVL
+
+	// Check the result - either string size or floating point 0 vs non-0
+
+	lda FAC1_exponent
+	beq_16 cmd_rem
+
+	// Condition fulfilled - look for GOTO or THEN
+
+	jsr fetch_character_skip_spaces
+	cmp #$89                           // 'GOTO'
+	beq_16 cmd_goto
+
+	cmp #$A7                           // 'THEN'
+	bne_16 do_SYNTAX_error
+
+	pla
+	pla
+
+	jmp execute_statements