started work on LET command

src/aliases/,aliases_ram_lowmem.s

@@ -46,7 +46,7 @@
 	.label DATLIN    = $3F // $3F-$40  -- NOT IMPLEMENTED --
 	.label DATPTR    = $41 // $41-$42  pointer for READ/DATA copmmands
 	.label INPPTR    = $43 // $43-$44  -- NOT IMPLEMENTED --
-	.label VARNAM    = $45 // $45-$46  -- NOT IMPLEMENTED --
+	.label VARNAM    = $45 // $45-$46  current variable name
 	.label VARPNT    = $47 // $47-$48  -- NOT IMPLEMENTED --
 	.label FORPNT    = $49 // $49-$4A  -- NOT IMPLEMENTED --
 	.label OPPTR     = $4B // $4B-$4C  helper variable for expression computation, [!] our usage details are different

src/basic/basic_commands/cmd__unimplemented.s

@@ -23,8 +23,6 @@ cmd_dim:
 	nop
 cmd_read:
 	nop
-cmd_let:
-	nop
 cmd_if:
 	nop
 cmd_gosub:

src/basic/basic_commands/cmd_let.s

@@ -0,0 +1,17 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+
+cmd_let:
+
+	// Fetch variable name, should be followed by assign operator
+
+	jsr fetch_variable
+	jsr injest_assign
+	bcs_16 do_SYNTAX_error
+
+	// XXX finish the implementation
+
+	jmp do_NOT_IMPLEMENTED_error

src/basic/engine/execute_line_statements.s

@@ -37,22 +37,22 @@ execute_statements:
 	ldx #$19
 	stx TEMPPT
 
-	// Check if token is valid for execution
-
-	cmp #$7F
-	bcc_16 execute_statements_var_assign         // not a token - try variable assign
-
 	// Move token code to .X
 
 	tax
 
-	// A token - first push the 'end_of_statement' address for RTS
+	// Push the 'end_of_statement' address for RTS
 
 	lda #>(end_of_statement - 1)
 	pha
 	lda #<(end_of_statement - 1)
 	pha
 
+	// Check if token is valid for execution
+
+	cpx #$7F
+	bcc_16 execute_statements_var_assign         // not a token - try variable assign
+
 	cpx #$A6
 	bcs execute_statements_extended
 
@@ -243,17 +243,18 @@ execute_line:
 
 execute_statements_var_assign:
 
-	// XXX here we should handle variable assignments, probably in a separate file
-
 	// Prevent wedges from being executed within a program
 
 #if CONFIG_TAPE_WEDGE
-	cmp #$40
+	cpx #$40
 	beq_16 do_DIRECT_MODE_ONLY_error
 #endif
 #if CONFIG_DOS_WEDGE
-	cmp #$5F
+	cpx #$5F
 	beq_16 do_DIRECT_MODE_ONLY_error
 #endif
 
-	jmp do_SYNTAX_error
+	// Try variable assignment - execute as LET command
+
+	jsr unconsume_character
+	jmp cmd_let

src/basic/engine/fetch_variable.s

@@ -0,0 +1,84 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+fetch_variable:
+
+	// Fetch variable name
+
+	lda #$00
+	sta VARNAM+1
+
+	// Fetch the first character
+!:
+	jsr fetch_character
+	cmp #$20                           // ignore all the spaces
+	beq !-
+
+	jsr fetch_variable_is_AZ
+	bcs_16 do_SYNTAX_error
+
+	sta VARNAM+0
+
+	// Fetch the (optional) second character
+
+	jsr fetch_character
+	jsr fetch_variable_is_09_AZ
+	bcs fetch_variable_check_type
+
+	sta VARNAM+1
+
+	// Fetch the remaining variable characters - ignore them
+!:
+	jsr fetch_character
+	jsr fetch_variable_is_09_AZ
+	bcc !-
+
+	// FALLTROUGH
+
+fetch_variable_check_type:
+
+	// Encode variable type within name, as documented in:
+	// - https://sites.google.com/site/h2obsession/CBM/basic/variable-format
+
+	cmp #$24                           // '$'
+	beq fetch_variable_type_string
+	cmp #$25                           // '%'
+	beq fetch_variable_type_integer
+
+	// FALLTORUGH
+
+fetch_variable_type_float:
+
+	jsr unconsume_character
+
+#if HAS_OPCODES_65C02
+	bra fetch_variable_find_addr
+#else
+	jmp fetch_variable_find_addr
+#endif
+
+fetch_variable_type_integer:
+
+	lda VARNAM+0
+	ora #$80
+	sta VARNAM+0
+
+	// FALLTROUGH
+
+fetch_variable_type_string:
+
+	lda VARNAM+1
+	ora #$80
+	sta VARNAM+1
+	
+	// FALLTROUGH
+
+fetch_variable_find_addr:
+
+	// Now try to find variable address
+
+	// XXX
+
+	rts

src/basic/engine/fetch_variable_is_09_AZ.s

@@ -0,0 +1,35 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Check .A content, if within 0-9, A-Z ranges, sets Carry if check fails
+//
+
+fetch_variable_is_09_AZ:
+
+	cmp #$41                                 // fail if below '0'
+	bcc fetch_variable_cmp_fail
+
+	cmp #$3A                                 // continue checking if above '9'
+	bcc fetch_variable_cmp_rts 
+
+	// FALLTROUGH
+
+fetch_variable_is_AZ:
+
+	cmp #$41                                 // fail if below 'A'
+	bcc fetch_variable_cmp_fail
+
+	cmp #$7B                                 // fail if above 'Z'
+
+	// FALLTROUGH
+
+fetch_variable_cmp_rts:
+
+	rts
+
+fetch_variable_cmp_fail:
+
+	sec
+	rts

src/basic/engine/injest_assign.s

@@ -0,0 +1,27 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Consummes assign operator in a BASIC code, Carry set if not found. Injests all spaces.
+//
+
+
+injest_assign:
+
+	jsr fetch_character
+	cmp #$B2                           // assign operator character
+	beq injest_assign_found
+	cmp #$20                           // space, can always be skipped
+	beq injest_assign
+	
+	// Not found
+	jsr unconsume_character
+
+	sec
+	rts
+
+injest_assign_found:
+
+	clc
+	rts