CompilerKit::Codegen

Codegen provides an API that can be used to create small but working bytecode programs using the virtual instruction set described in Program. It follows Program’s stack-based model, and abstracts away labels, jumps, loops, constants and variables.

For example, emitting a program that loops would look like this, when called from a recursive descent parser:

Codegen gen;

gen.startLoop();

// This function should emit code that leaves the boolean result on the stack.
recBooleanExpr();

gen.startLoopBody();

// ...
// Here goes the contents of your loop.
// ...
recStatementBlock();

gen.endLoop();

Public API

`Codegen()`

Creates a new Codegen instance.

`getProgram() -> Program`

Returns the bytecode program that has been generated.

`emit(Instruction instr, ...) -> void`

emit(Instruction instr) -> void (1)
emit(Instruction instr, uint8_t operand) -> void (2)
emit(Instruction instr, uint16_t operand) -> void (3)

Emits one instruction (1), along its 8-bit (2) or 16-bit (3) operand.

Parameters:

instr: a byte code instruction (see Program for listing).
operand (optional): a 8-bit or 16-bit integer operand to instr.

`emitConst(float value) -> void`

Adds a constant numeric value to the program, and emits the bytecode instruction to load it (Instruction::Const).

Parameters:

value: the constant’s numeric value.

`startLoop() -> void`

Marks the start of a loop’s condition. This must be called right before emitting the bytecode for the boolean expression driving the loop.

`startLoopBody() -> void`

Marks the end of a loop’s condition, and the beginning of its body. This should be called right after emitting the bytecode for the boolean expression driving the loop, and expect a boolean value to have been pushed on top of the operand stack.

`endLoop() -> void`

Marks the end of a loop’s body.

`startConditonal() -> void`

Marks the start of a conditonal statement. This must be called right before emitting the bytecode for the boolean expression used by the conditional.

`startIfBody() -> void`

Marks the end of a conditional statement’s condition, and the start of the true case’s body. This must be called right after emitting the bytecode for the boolean expression used by the conditional.

`startElseBody() -> void`

Marks the end of a conditional statement’s condition, and the start of the false case’s body. This section is optional.

If an else if(...) {...} statement is desired, a call to startConditional() can be made after.

`endConditional() -> void`

Marks the end of a conditional statement. Note that conditional statements can be nested: there must be as many calls to endConditional as there were to startConditional.