more work on variables support

src/aliases/,aliases_ram_lowmem.s

@@ -47,7 +47,7 @@
 	.label DATPTR    = $41 // $41-$42  pointer for READ/DATA copmmands
 	.label INPPTR    = $43 // $43-$44  -- NOT IMPLEMENTED --
 	.label VARNAM    = $45 // $45-$46  current variable name
-	.label VARPNT    = $47 // $47-$48  -- NOT IMPLEMENTED --
+	.label VARPNT    = $47 // $47-$48  current variable/descriptor pointer
 	.label FORPNT    = $49 // $49-$4A  -- NOT IMPLEMENTED --
 	.label OPPTR     = $4B // $4B-$4C  helper variable for expression computation, [!] our usage details are different
 	.label OPMASK    = $4D //          -- NOT IMPLEMENTED --

src/basic/basic_commands/cmd_let.s

@@ -12,6 +12,73 @@ cmd_let:
 	jsr injest_assign
 	bcs_16 do_SYNTAX_error
 
+	// Determine variable type and push it to the stack
+
+	lda #$00
+	clc
+	bit VARNAM+0
+	bpl !+
+	adc #$01
+!:
+	bit VARNAM+1
+	bpl !+
+	adc #$80
+!:
+	pha
+
+	// Push the VARPNT to the stack - it might get overridden
+
+	lda VARPNT+0
+	pha
+	lda VARPNT+1
+	pha
+
+	// Evaluate the expression
+
+	jsr FRMEVL
+
+	// Restore VARPNT
+
+	pla
+	sta VARPNT+1
+	pla
+	sta VARPNT+0
+
+	// Determine what to assign
+
+	pla
+	bmi cmd_let_assign_string
+	beq cmd_let_assign_float
+
+	// FALLTROUGH
+
+	// XXX integer and float probably have much in common
+
+cmd_let_assign_integer:
+
+	lda VALTYP
+	bmi_16 do_TYPE_MISMATCH_error
+
+	// XXX finish the implementation
+
+	jmp do_NOT_IMPLEMENTED_error
+
+cmd_let_assign_float:
+
+	lda VALTYP
+	bmi_16 do_TYPE_MISMATCH_error
+
+	// XXX finish the implementation
+
+	jmp do_NOT_IMPLEMENTED_error
+
+cmd_let_assign_string:
+
+	// Check if value type matches
+	
+	lda VALTYP
+	bpl_16 do_TYPE_MISMATCH_error
+
 	// XXX finish the implementation
 
 	jmp do_NOT_IMPLEMENTED_error

src/basic/engine/fetch_variable.s

@@ -77,8 +77,135 @@ fetch_variable_type_string:
 
 fetch_variable_find_addr:
 
-	// Now try to find variable address
+	// Now try to find variable address between VARTAB and ARYTAB, see
+	// - https://www.c64-wiki.com/wiki/Memory_(BASIC)
+
+	lda VARTAB+0
+	sta VARPNT+0
+	lda VARTAB+1
+	sta VARPNT+1
+
+	// FALLTROUGH
+
+fetch_variable_find_addr_loop:
+
+	// Check if end of search loop
+
+	lda VARPNT+1
+	cmp ARYTAB+1
+	bne !+
+	lda VARPNT+0
+	cmp VARPNT+0
+	beq fetch_variable_alocate
+!:
+	// Compare current variable name with searched one
+	// XXX consider creating optimized version for 46K/50K memory models
+
+	ldy #$00
+
+#if CONFIG_MEMORY_MODEL_60K
+	ldx #<VARPNT
+	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_VARPNT
+#else // CONFIG_MEMORY_MODEL_38K
+	lda (VARPNT),y
+#endif
+
+	cmp VARNAM+0
+	bne fetch_variable_find_addr_next
+
+	iny
+
+#if CONFIG_MEMORY_MODEL_60K
+	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_VARPNT
+#else // CONFIG_MEMORY_MODEL_38K
+	lda (VARPNT),y
+#endif
+
+	cmp VARNAM+1
+	bne fetch_variable_find_addr_next
+
+	// FALLTROUGH
+
+fetch_variable_adjust_VARPNT:
+
+	// Adjust VARPNT to point just after variable name and quit
+
+#if !HAS_OPCODES_65CE02
+
+	clc
+	lda VARPNT+0
+	adc #$02
+	sta VARPNT+0
+	bcc !+
+	inc VARPNT+1
+!:
+#else // HAS_OPCODES_65CE02
+
+	inw VARPNT
+	inw VARPNT
+
+#endif
+
+	rts
+
+fetch_variable_find_addr_next:
+
+	// Increase VARPNT by 7 - constant value, each variable uses 7 bytes, see:
+	// - https://sites.google.com/site/h2obsession/CBM/basic/variable-format
+
+	clc
+	lda VARPNT+0
+	adc #$07
+	sta VARPNT+0
+	bcc fetch_variable_find_addr_loop
+	inc VARPNT+1
+	bne fetch_variable_find_addr_loop  // branch always
+
+fetch_variable_alocate:
+	
+	// First check if we have enough space for a new descriptor
 
 	// XXX
 
-	rts
+	// If needed, move all the arrays up
+
+	// XXX
+
+	// Set pointer to new variable
+
+	// XXX
+
+	// Fill-in the new variable name, descriptor (it is enough to zero first 2 bytes of content)
+
+	ldy #$00
+
+#if CONFIG_MEMORY_MODEL_60K
+	
+	// XXX
+
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	
+	lda VARNAM+0
+	sta (VARPNT),y
+	iny
+	lda VARNAM+1
+	sta (VARPNT),y
+	iny
+	lda #$00
+	sta (VARPNT),y
+	iny
+	sta (VARPNT),y
+
+#endif
+
+	// Adjust variable pointer and quit
+
+#if HAS_OPCODES_65C02
+	bra fetch_variable_adjust_VARPNT
+#else
+	jmp fetch_variable_adjust_VARPNT
+#endif

src/basic/engine/varstr_garbage_collect.s

@@ -259,11 +259,7 @@ varstr_garbage_collect_check_bptr:
 
 	// Next iteration
 
-#if HAS_OPCODES_65C02
-	bra varstr_garbage_collect_loop
-#else
 	jmp varstr_garbage_collect_loop
-#endif
 
 varstr_garbage_collect_unused:
 
@@ -299,11 +295,7 @@ varstr_garbage_collect_unused:
 
 	// Next iteration
 
-#if HAS_OPCODES_65C02
-	bra varstr_garbage_collect_loop
-#else
 	jmp varstr_garbage_collect_loop
-#endif
 
 
 

src/basic/memory/under_rom_peek_poke_46k_50k.s

@@ -51,6 +51,23 @@ peek_under_roms_via_OLDTXT:
 	jmp peek_under_roms_finalize
 #endif
 
+peek_under_roms_via_VARPNT:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Retrieve value from under ROMs
+
+	lda (VARPNT), y
+
+#if HAS_OPCODES_65C02
+	bra peek_under_roms_finalize
+#else
+	jmp peek_under_roms_finalize
+#endif
+
 peek_under_roms_via_DSCPNT:
 
 	// Unmap BASIC lower ROM