Nand2Tetris Jack Constructor VM Mapping

Nand2Tetris Common Issues

../../tools/JackCompiler.bat Fraction/

Compiling "C:\Users....\09\Fraction\"
Could not find file or directory: C:\Users..

Problem - the '/' provided along with directory name. Yes, lame, I know :) Shimon's response : our purpose is didactic, not production :)

while( 1 ) {

}

use while( true ) ...

Aha - API claims drawCircle can handle radius of 181... Nice try there. I just found out you have to stay below 128 (127 is ok)

In Circle.jack (line 23): In subroutine PlotCircle: Expected (

Most likely reason - you used a "do" when you meant to use "let" :) Don't you miss Perl's errors/warnings :) ?

Gotcha - you HAVE to declare ALL variables before any "action".

var int xyz;
let xyz = 0;
var int pqr;

won't fly :)

Jack Programming Helpers

Jack Peculiarities

° The keyword let:
must be used in assignments: let x = 0;
° The keyword do:
must be used for calling a method or a function outside an expression:
do reduce();
° The body of a statement must be within curly brackets, even if it
contains a single statement: if (a > a) {return 3} else {return -a};
° All subroutine must end with a return
° N0 operator priority:
-- The following value if unpredictable: 2 + 3 * 4
-- To enforce priority of operations, use parentheses: 2 + (3 * 4)
° The language is weakly typed

Jack Language Cheat Sheet

class, constructor, method, function Program components
int, boolean, char, void Primitive types

var, static, field Variable declarations
let, do, if, else, while, return Statements

true, false, null Constant values


this Object reference