first step towards string expression evaluation

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"

c64/basic/engine/ad9e.interop

@@ -0,0 +1,3 @@
+
+This routine is desribed in Mapping the C64, page 102, and used at least by CCGMS terminal software - see here:
+- https://raw.githubusercontent.com/spathiwa/ccgmsterm/master/original/5a.gs