Evaluators

The compiler, bitterasm, never produces machine code. It runs a program and records the values it emits, in order, in a .em file. An evaluator reads that file and decides what the values mean.

prog.basm ──bitterasm compile──▶ prog.em ──evaluator──▶ output

bitter is the evaluator that ships with BitterASM. It packs values into bytes: binary machine code, or an executable. See Packing bytes with bitter.

Why split it this way

The language never assumes a program’s output is binary. A bits<8> is a struct from the standard library, not a language feature. Only bitter knows that bits<8> means “eight bits.”

So a different evaluator could read the same .em file and produce something else entirely: a hex dump for a teaching tool, a listing, words for a 36-bit machine, trits for a ternary one. The language, and every library that doesn’t depend on bitter, stays the same.

Which types an evaluator knows

In .em, every struct and enum is identified by its module path and name, such as std.binary.bits. An evaluator gives meaning to the ids it knows, and treats everything else however its contract says. bitter knows a handful of ids from std.binary and std.bitter, and packs any other struct as the concatenation of its fields.

In this chapter

• The .em format: the specification an evaluator reads.
• Packing bytes with bitter: how bitter turns values into bytes.