From 48eec7d56e8bc6ccd9a1a5b1aa9503a0c4574d0a Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Sat, 6 Jun 2020 19:16:54 +0200
Subject: [PATCH] first step towards string expression evaluation

---
 c64/aliases/,aliases_ram_lowmem.s         |  2 +-
 c64/basic/,stubs/ad9e.frmevl.s            | 10 -----
 c64/basic/commands/cmd_print.s            | 50 ++++++++++++++++++++++-
 c64/basic/engine/ad9e.frmevl.s            | 40 ++++++++++++++++++
 c64/basic/{,stubs => engine}/ad9e.interop |  0
 5 files changed, 89 insertions(+), 13 deletions(-)
 delete mode 100644 c64/basic/,stubs/ad9e.frmevl.s
 create mode 100644 c64/basic/engine/ad9e.frmevl.s
 rename c64/basic/{,stubs => engine}/ad9e.interop (100%)

diff --git a/c64/aliases/,aliases_ram_lowmem.s b/c64/aliases/,aliases_ram_lowmem.s
index 2f1cbb06..acb718d5 100644
--- a/c64/aliases/,aliases_ram_lowmem.s
+++ b/c64/aliases/,aliases_ram_lowmem.s
@@ -20,7 +20,7 @@
 	.label VERCKB    = $0A //          flag used by BASIC, 0 - LOAD, 1 - VERIFY
 	.label COUNT     = $0B //          [!] our implementation might be different  XXX give more details
 	.label DIMFLG    = $0C //          [!] our implementation might be different  XXX give more details
-	.label VALTYP    = $0D //          -- NOT IMPLEMENTED --
+	.label VALTYP    = $0D //          expression eveluation result; $00 - float, $FF - string
 	.label INTFLG    = $0E //          -- NOT IMPLEMENTED --
 	.label GARBFL    = $0F //          [!] our implementation might be different  XXX give more details
 	.label SUBFLG    = $10 //          -- NOT IMPLEMENTED --
diff --git a/c64/basic/,stubs/ad9e.frmevl.s b/c64/basic/,stubs/ad9e.frmevl.s
deleted file mode 100644
index 46f275ed..00000000
--- a/c64/basic/,stubs/ad9e.frmevl.s
+++ /dev/null
@@ -1,10 +0,0 @@
-// #LAYOUT# STD *       #TAKE
-// #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
-// #LAYOUT# *   BASIC_0 #TAKE
-// #LAYOUT# *   *       #IGNORE
-
-
-// XXX provide documentation and implementation
-
-FRMEVL:
-	STUB_IMPLEMENTATION()
diff --git a/c64/basic/commands/cmd_print.s b/c64/basic/commands/cmd_print.s
index 85bf7d96..d9fd8b16 100644
--- a/c64/basic/commands/cmd_print.s
+++ b/c64/basic/commands/cmd_print.s
@@ -6,8 +6,50 @@
 
 cmd_print:
 
-	// XXX print an argument here
+	// First check if we have anything to print
 
+	jsr end_of_statement_check
+	bcs cmd_print_new_line
+
+	cmp #$3B                           // semicolon
+	beq cmd_print_done
+
+	jsr unconsume_character
+
+	// FALLTROUGH
+
+cmd_print_loop:
+
+	// Now evaluate the expression
+
+	jsr FRMEVL
+	lda VALTYP
+	bpl cmd_print_float
+
+	// FALLTROUGH
+
+cmd_print_string:
+
+	// Print a string value
+
+	ldy #$00
+!:
+	cpy __FAC1 + 0
+	beq cmd_print_next_arg
+
+	lda (__FAC1 + 1), y                // XXX read from under ROM
+	jsr JCHROUT
+	iny
+	jmp !-
+
+cmd_print_float:
+
+	// XXX probably we should also check INTFLG here
+	// XXX
+
+	// FALLTROUGH
+
+cmd_print_next_arg:
 
 	// Look for the next argument
 
@@ -16,10 +58,14 @@ cmd_print:
 
 	jsr fetch_character
 	cmp #$2C                           // comma
-	beq cmd_print
+	beq cmd_print_loop
 	cmp #$3B                           // semicolon
 	beq cmd_print_done
 
+	// Something unexpected
+
+	jmp do_SYNTAX_error
+
 cmd_print_new_line:
 
 	jsr print_return
diff --git a/c64/basic/engine/ad9e.frmevl.s b/c64/basic/engine/ad9e.frmevl.s
new file mode 100644
index 00000000..be7fb23b
--- /dev/null
+++ b/c64/basic/engine/ad9e.frmevl.s
@@ -0,0 +1,40 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+// Well-known BASIC routine, described in:
+//
+// - [CM64] Computes Mapping the Commodore 64 - page 102
+// - https://sta.c64.org/cbm64basconv.html
+//
+// Output:
+// - VALTYP - $00 = floating number, $FF = string
+// - INTFLG (XXX float/integer, probably)
+// - for float: FAC1
+// - for string: __FAC1 + 0 = length, __FAC1 + 1 = pointer to string
+
+// XXX provide documentation and implementation
+
+FRMEVL:
+
+	// XXX for now we just report dummy string
+
+	lda #$FF
+	sta VALTYP
+
+	lda #$0B
+	sta __FAC1 + 0
+
+	lda #<dummy_text
+	sta __FAC1 + 1
+
+	lda #>dummy_text
+	sta __FAC1 + 2
+
+	rts
+
+dummy_text:
+
+	.text "LOREM IPSUM"
diff --git a/c64/basic/,stubs/ad9e.interop b/c64/basic/engine/ad9e.interop
similarity index 100%
rename from c64/basic/,stubs/ad9e.interop
rename to c64/basic/engine/ad9e.interop