LEN function, FONT statement - loading custom fonts! (see docs)

README.md

@@ -9,10 +9,11 @@ Compiler structure and engine is heavily inspired by [Let's Build a Compiler, by
 * Boolean operators: & ~ !
 * Bit shifts: << >>
 * Relational operators: == <> < > <= >=
+* Loading custom fonts
 * Control structures: IF, LOOP
 * Variables (both integer and string)
-* Statements: CLS, LOCATE, PRINT, COLOR, KEY, INPUT, POKE, GOTO, RND
-* Functions: STR, CHR, VAL, PEEK, SQR
+* Statements: CLS, LOCATE, PRINT, COLOR, KEY, INPUT, POKE, GOTO, RND, FONT
+* Functions: STR, CHR, VAL, LEN, PEEK, SQR
 
 ## How the language looks like
 
@@ -177,6 +178,17 @@ Number = VAL(expression)
 
 Returns an integer representation of a number in string variable (e.g. input from user)
 
+### LEN
+
+Usage:
+
+```
+DIM Length
+Length = LEN(expression)
+```
+
+Returns length (how many letters) of a string.
+
 ### INPUT
 
 Usage:
@@ -250,6 +262,18 @@ Result = SQR(expression)
 
 Computes square root of _expression_.
 
+### FONT
+
+Usage:
+
+```
+FONT "file.txt"
+```
+
+Loads custom font from text file and replaces current terminal font with it. Font file can specify only selected characters.  
+For a sample font file please refer to _fonts/box.txt_ file. Every letter in font file starts with letter ascii code, and then 8 lines 4 character each follow,
+where dot (.) is an empty space and capital o (O) is a solid "pixel".
+
 ### END
 
 Program MUST end with an ```END``` statement.

asm.go

@@ -264,7 +264,7 @@ func Poke() {
 
 func PutChar() {
 	SkipWhite()
-	if (Look == '"') {
+	if Look == '"' {
 		GetChar()
 		EmitLine(fmt.Sprintf("SET [0x8000+X], %d", Look))
 		GetChar()
@@ -281,6 +281,16 @@ func PutChar() {
 	EmitLine("AND X, 0x1ff")
 }
 
+func Font() {
+	SkipWhite()
+	if Look == '"' {
+		Next()
+		LoadFont(Value)
+		Token = '$'
+		Next()
+	}
+}
+
 func Goto() {
 	Next()
 	Token = '$'
@@ -292,6 +302,53 @@ func Input() {
 	Call("input")
 }
 
+func LoadFont(filename string) {
+	var error error
+	var file *os.File
+	var charCode = 0
+	var charLine uint8 = 0
+	var charWord1 uint32 = 0
+	var charWord2 uint32 = 0
+
+	EmitLine(fmt.Sprintf("; loading font: %s", filename))
+	file, error = os.Open(filename)
+	if error != nil {
+		Error(fmt.Sprintf("Couldn't open '%s' font file!", filename))
+		return
+	}
+	reader := bufio.NewReader(file)
+	for {
+		line, _, error := reader.ReadLine()
+		if error != nil {
+			break
+		}
+		if len(line) < 4 {
+			charCode, _ = strconv.Atoi(string(line))
+			charWord1 = 0
+			charWord2 = 0
+			charLine = 0
+		} else {
+			if line[0] == 'O' {
+				charWord1 = charWord1 | (1 << (charLine + 8))
+			}
+			if line[1] == 'O' {
+				charWord1 = charWord1 | (1 << charLine)
+			}
+			if line[2] == 'O' {
+				charWord2 = charWord2 | (1 << (charLine + 8))
+			}
+			if line[3] == 'O' {
+				charWord2 = charWord2 | (1 << charLine)
+			}
+			charLine++
+			if (charLine == 8) {
+				EmitLine(fmt.Sprintf("SET [%#x], %#x", 0x8180 + charCode * 2, charWord1))
+				EmitLine(fmt.Sprintf("SET [%#x], %#x", 0x8181 + charCode * 2, charWord2))
+			}
+		}
+	}
+}
+
 func Lib() {
 	var error error
 	var file *os.File

fonts/box.txt

@@ -0,0 +1,27 @@
+6
+O.O.
+O.O.
+O.O.
+..O.
+OOO.
+....
+....
+....
+7
+....
+....
+OOO.
+..O.
+O.O.
+O.O.
+O.O.
+O.O.
+15
+O.O.
+O.O.
+O.O.
+O.O.
+O.O.
+O.O.
+O.O.
+O.O.

functions.go

@@ -57,3 +57,9 @@ func FuncSqr() {
 	Call("sqrt")
 }
 
+func FuncLen() {
+	Next()
+	MatchString("(")
+	BoolExpression()
+	Call("strlen")
+}

lib.dasm

@@ -23,7 +23,7 @@
 	SET B, A
 	SET A, 0
 	:strlen1
-	IFN [B], 0  ; if character is 00 - end of string
+	IFE [B], 0  ; if character is 00 - end of string
 	SET PC, POP ; end function
 	ADD A, 1 ; increment char count
 	ADD B, 1 ; increment char address