Allow mutable function arguments

examples/raytracer.psl

@@ -19,12 +19,11 @@ func print_byte(c: u8):
 	foreign func putchar(c: i32) -> i32
 	putchar(c as i32)
 
-func print_str(str: u8*):
+func print_str(mut str: u8*):
 	// Don't use puts() because it adds a newline
-	mut p = str
-	while *p != 0ub:
-		print_byte(*p)
-		p += 1
+	while *str != 0ub:
+		print_byte(*str)
+		str += 1
 
 func print_i32(x: i32):
 	if x < 0:
@@ -35,7 +34,7 @@ func print_i32(x: i32):
 		print_i32(x / 10)
 	print_byte('0' + (x % 10 as u8))
 
-func print_f32(x: f32):
+func print_f32(mut x: f32):
 	if x < 0.0:
 		print_byte('-')
 		print_f32(-x)
@@ -44,14 +43,14 @@ func print_f32(x: f32):
 	let xfloor = floor(x)
 	print_i32(xfloor)
 	print_byte('.')
-	mut y = x - (xfloor as f32)
+	x -= (xfloor as f32)
 	// Print fractional part
 	mut i = 0
 	while i < 3:
-		y = y * 10.0
-		let yfloor = floor(y)
-		print_byte('0' + (yfloor as u8))
-		y = y - (yfloor as f32)
+		x = x * 10.0
+		let xfloor = floor(x)
+		print_byte('0' + (xfloor as u8))
+		x -= (xfloor as f32)
 		i = i + 1
 
 func print_vec3(v: vec3):
@@ -108,8 +107,8 @@ struct file:
 func open(path: u8*, mode: u8) -> file*:
 	foreign func fopen(path: u8*, mode: u8*) -> file*
 	// A hack to turn a single u8 into a zero-terminated array
-	let mode_wide = mode as u32
-	return fopen(path, &mode as u8*)
+	let mode_wide = [mode, 0ub]
+	return fopen(path, &mode_wide as u8*)
 
 func close(file: file*):
 	foreign func fclose(file: file*) -> i32

libs/parser/rules/pslang.y

@@ -275,6 +275,7 @@ nonempty_function_declaration_argument_list
 
 function_declaration_single_argument
 : name colon type_expression { $$ = ast::function_declaration::argument{ast::value_category::constant, $1, std::make_unique<ast::type>($3), @$}; }
+| mut name colon type_expression { $$ = ast::function_declaration::argument{ast::value_category::_mutable, $2, std::make_unique<ast::type>($4), @$}; }
 ;
 
 function_return_type