AST to Bytecode

Lower an expression AST into a stack-based bytecode sequence.

This is a tiny compiler backend step: take structured AST nodes and produce a linear instruction list.

Function signature

func Lower(expr *Expr) []Instr

AST shape

Use the provided Expr struct with these conventions:

• ExprNumber: Value holds the number lexeme
• ExprIdent: Value holds the identifier name
• ExprUnary: Value holds the operator, Left holds the operand
• ExprBinary: Value holds the operator, Left and Right hold operands
• ExprCall: Value holds the function name, Args holds arguments

Bytecode rules

Emit instructions in postfix (stack) order:

• Number: PUSH_NUM <value>
• Identifier: PUSH_IDENT <name>
• Unary: lower operand, then NEG or NOT
• Binary: lower left, lower right, then the operator
• Call: lower args left-to-right, then CALL <name> <arity>

Operators map to opcodes as follows:

• + -> ADD
• - -> SUB
• * -> MUL
• / -> DIV
• == -> EQ
• != -> NEQ
• < -> LT
• <= -> LTE
• > -> GT
• >= -> GTE
• unary - -> NEG
• unary ! -> NOT

Notes

• Parse numbers with base-10 integer conversion.
• The output should be readable and deterministic.