elysium/backend_wat.go

package main

import (
	"errors"
	"fmt"
	"strconv"
	"unicode"
)

const COMPILE_OPTION_NO_BOUNDS_CHECK = "no_bounds_check"

type Compiler struct {
	Files          []*ParsedFile
	Wasm64         bool
	CompileOptions map[string]string

	CurrentBlock    *Block
	CurrentFunction *ParsedFunction
}

func getPrimitiveWATType(primitive PrimitiveType) string {
	switch primitive {
	case Primitive_I8, Primitive_I16, Primitive_I32, Primitive_U8, Primitive_U16, Primitive_U32:
		return "i32"
	case Primitive_I64, Primitive_U64:
		return "i64"
	case Primitive_F32:
		return "f32"
	case Primitive_F64:
		return "f64"
	case Primitive_Bool:
		return "i32"
	}

	panic(fmt.Sprintf("unhandled type in getPrimitiveWATType(): %s", primitive))
}

func safeASCIIIdentifier(identifier string) string {
	ascii := ""
	for _, rune := range identifier {
		if rune < unicode.MaxASCII && (unicode.IsLetter(rune) || unicode.IsDigit(rune)) {
			ascii += string(rune)
			continue
		}

		ascii += "$" + strconv.Itoa(int(rune))
	}

	return ascii
}

func getTypeCast(primitive PrimitiveType) Code {
	switch primitive {
	case Primitive_I8:
		return ofInstruction("i32.extend8_s")
	case Primitive_U8:
		return ofInstruction("i32.const 255", "i32.and")
	case Primitive_I16:
		return ofInstruction("i32.extend16_s")
	case Primitive_U16:
		return ofInstruction("i32.const 65535", "i32.and")
	case Primitive_Bool:
		return ofInstruction("i32.const 0", "i32.ne")
	}

	return emptyCode()
}

func pushConstantNumberWAT(primitive PrimitiveType, value any) Code {
	switch primitive {
	case Primitive_I8, Primitive_I16, Primitive_I32:
		return ofInstruction("i32.const " + strconv.FormatInt(value.(int64), 10))
	case Primitive_U8, Primitive_U16, Primitive_U32:
		return ofInstruction("i32.const " + strconv.FormatUint(value.(uint64), 10))
	case Primitive_I64:
		return ofInstruction("i64.const " + strconv.FormatInt(value.(int64), 10))
	case Primitive_U64:
		return ofInstruction("i64.const " + strconv.FormatUint(value.(uint64), 10))
	case Primitive_F32:
		return ofInstruction("f32.const " + strconv.FormatFloat(value.(float64), 'f', -1, 32))
	case Primitive_F64:
		return ofInstruction("f64.const " + strconv.FormatFloat(value.(float64), 'f', -1, 64))
	}

	panic(fmt.Sprintf("invalid type passed to pushConstantNumberWAT(): %s", primitive))
}

func (c *Compiler) getAddressWATType() string {
	if c.Wasm64 {
		return "i64"
	} else {
		return "i32"
	}
}

func (c *Compiler) getEffectiveAddressType() PrimitiveType {
	if c.Wasm64 {
		return Primitive_U64
	} else {
		return Primitive_U32
	}
}

func (c *Compiler) getWATType(t Type) string {
	switch t.Type {
	case Type_Primitive:
		return getPrimitiveWATType(t.Value.(PrimitiveType))
	case Type_Named, Type_Array:
		return c.getAddressWATType()
	case Type_Tuple:
		panic(fmt.Sprintf("tuple type passed to getWATType(): %s", t))
	}

	panic(fmt.Sprintf("type not implemented in getWATType(): %s", t))
}

func (c *Compiler) getPrimitiveTypeSizeBytes(primitive PrimitiveType) int {
	switch primitive {
	case Primitive_I8, Primitive_U8, Primitive_Bool:
		return 1
	case Primitive_I16, Primitive_U16:
		return 2
	case Primitive_I32, Primitive_U32, Primitive_F32:
		return 4
	case Primitive_I64, Primitive_U64, Primitive_F64:
		return 8
	}

	panic(fmt.Sprintf("unhandled type in getPrimitiveTypeSizeBytes(): %s", primitive))
}

func (c *Compiler) getTypeSizeBytes(t Type) int {
	switch t.Type {
	case Type_Primitive:
		return c.getPrimitiveTypeSizeBytes(t.Value.(PrimitiveType))
	case Type_Named, Type_Array:
		return c.getPrimitiveTypeSizeBytes(Primitive_U64)
	case Type_Tuple:
		panic(fmt.Sprintf("tuple type passed to getTypeSizeBytes(): %s", t))
	}

	panic(fmt.Sprintf("unhandled type in getTypeSizeBytes(): %s", t))
}

func castPrimitiveWAT(from PrimitiveType, to PrimitiveType) (Code, error) {
	if from == to {
		return emptyCode(), nil
	}

	if from == Primitive_Bool || to == Primitive_Bool {
		return emptyCode(), errors.New("cannot upcast from or to bool")
	}

	fromFloat := isFloatingPoint(from)
	toFloat := isFloatingPoint(to)
	if fromFloat && toFloat {
		if to == Primitive_F32 {
			return ofInstruction("f32.demote_f64"), nil
		} else {
			return ofInstruction("f64.promote_f32"), nil
		}
	}

	if toFloat {
		var suffix string

		if isUnsignedInt(to) {
			suffix = "u"
		} else {
			suffix = "s"
		}

		return ofInstruction(getPrimitiveWATType(to) + ".convert_" + getPrimitiveWATType(from) + "_" + suffix), nil
	}

	if fromFloat {
		var suffix string

		if isUnsignedInt(to) {
			suffix = "u"
		} else {
			suffix = "s"
		}

		return ofInstruction(getPrimitiveWATType(to) + ".trunc_" + getPrimitiveWATType(from) + "_" + suffix), nil
	}

	if getBits(from) == getBits(to) {
		return emptyCode(), nil
	}

	if getPrimitiveWATType(from) == getPrimitiveWATType(to) {
		if getBits(to) < getBits(from) {
			return getTypeCast(to), nil
		}

		return emptyCode(), nil
	}

	if getBits(from) < 64 && getBits(to) == 64 {
		var suffix string

		if isUnsignedInt(from) {
			suffix = "u"
		} else {
			suffix = "s"
		}

		return ofInstruction("i64.extend_i32_" + suffix), nil
	}

	code := ofInstruction("i32.wrap_i64")
	code.addAll(getTypeCast(to))
	return code, nil
}

func (c *Compiler) compileAssignmentExpressionWAT(assignment AssignmentExpression) (Code, error) {
	lhs := assignment.Lhs

	exprWAT, err := c.compileExpressionWAT(assignment.Value)
	if err != nil {
		return emptyCode(), err
	}

	switch lhs.Type {
	case Expression_VariableReference:
		ref := lhs.Value.(VariableReferenceExpression)
		local := strconv.Itoa(getLocal(c.CurrentBlock, ref.Variable).Index)

		exprWAT.add("local.tee $" + local + " (;" + ref.Variable + ";)")
		return exprWAT, nil
	case Expression_ArrayAccess:
		array := lhs.Value.(ArrayAccessExpression)

		localArray := Local{Name: "", Type: Type{Type: Type_Primitive, Value: c.getEffectiveAddressType(), Position: unknownPosition()}, IsParameter: false, Index: len(c.CurrentFunction.Locals)}
		c.CurrentFunction.Locals = append(c.CurrentFunction.Locals, localArray)

		localIndex := Local{Name: "", Type: Type{Type: Type_Primitive, Value: c.getEffectiveAddressType(), Position: unknownPosition()}, IsParameter: false, Index: len(c.CurrentFunction.Locals)}
		c.CurrentFunction.Locals = append(c.CurrentFunction.Locals, localIndex)

		localElement := Local{Name: "", Type: *assignment.Value.ValueType, IsParameter: false, Index: len(c.CurrentFunction.Locals)}
		c.CurrentFunction.Locals = append(c.CurrentFunction.Locals, localElement)

		arrayWAT, err := c.compileExpressionWAT(array.Array)
		if err != nil {
			return emptyCode(), err
		}

		arrayWAT.add("local.set $" + strconv.Itoa(localArray.Index) + " (;array base address;)")

		indexWAT, err := c.compileExpressionWAT(array.Index)
		if err != nil {
			return emptyCode(), err
		}

		if !c.Wasm64 {
			cast, err := castPrimitiveWAT(Primitive_I64, Primitive_I32)
			if err != nil {
				return emptyCode(), err
			}

			indexWAT.addAll(cast)
		}

		indexWAT.add("local.set $" + strconv.Itoa(localIndex.Index) + " (;array index;)")

		wat := concat(arrayWAT, indexWAT)

		if _, ok := c.CompileOptions[COMPILE_OPTION_NO_BOUNDS_CHECK]; !ok {
			// Error if index < 0
			wat.add(
				"block",
				"local.get $"+strconv.Itoa(localIndex.Index)+" (;array index;)",
				c.getAddressWATType()+".const 0",
				c.getAddressWATType()+".ge_s",
				"br_if 0",
				"call $__builtin_panic",
				"end",
			)

			// Error if index >= array length
			wat.add(
				"block",
				"local.get $"+strconv.Itoa(localIndex.Index)+" (;array index;)",
				"local.get $"+strconv.Itoa(localArray.Index)+" (;array base address;)",
				"i32.load", // Load array length
				c.getAddressWATType()+".lt_s",
				"br_if 0",
				"call $__builtin_panic",
				"end",
			)
		}

		elementType := array.Array.ValueType.Value.(ArrayType).ElementType
		wat.add(
			"local.get $"+strconv.Itoa(localIndex.Index)+" (;array index;)",
			c.getAddressWATType()+".const "+strconv.Itoa(c.getTypeSizeBytes(elementType)),
			c.getAddressWATType()+".mul",
			"local.get $"+strconv.Itoa(localArray.Index)+" (;array base address;)",
			c.getAddressWATType()+".add",
			c.getAddressWATType()+".const 4", // first 4 bytes = length
			c.getAddressWATType()+".add",
		)

		wat.addAll(exprWAT)

		wat.add(
			"local.tee $"+strconv.Itoa(localElement.Index),
			c.getWATType(elementType)+".store", // TODO: use load8/load16(_s/u) for smaller types
			"local.get $"+strconv.Itoa(localElement.Index),
		)

		return wat, nil
	case Expression_RawMemoryReference:
		raw := lhs.Value.(RawMemoryReferenceExpression)

		local := Local{Name: "", Type: *lhs.ValueType, IsParameter: false, Index: len(c.CurrentFunction.Locals)}
		c.CurrentFunction.Locals = append(c.CurrentFunction.Locals, local)

		if raw.Type.Type != Type_Primitive {
			panic("TODO") //TODO
		}

		addrWAT, err := c.compileExpressionWAT(raw.Address)
		if err != nil {
			return emptyCode(), err
		}

		// TODO: should leave a copy of the stored value on the stack
		code := addrWAT.clone()
		code.addAll(exprWAT)
		code.add(
			"local.tee $"+strconv.Itoa(local.Index),
			c.getWATType(raw.Type)+".store",
			"local.get $"+strconv.Itoa(local.Index),
		)

		return code, nil
	}

	panic("assignment expr not implemented")
}

func (c *Compiler) compileAssignmentUpdateExpressionWAT(lhs Expression, updateWAT Code, evaluateToOldValue bool) (Code, error) {
	switch lhs.Type {
	case Expression_VariableReference:
		ref := lhs.Value.(VariableReferenceExpression)
		local := strconv.Itoa(getLocal(c.CurrentBlock, ref.Variable).Index)

		exprWAT, err := c.compileExpressionWAT(lhs)
		if err != nil {
			return emptyCode(), err
		}

		wat := exprWAT.clone()
		if evaluateToOldValue {
			wat.add("local.get $" + local + " (;" + ref.Variable + ";)")
		}

		wat.addAll(updateWAT)

		if evaluateToOldValue {
			wat.add("local.set $" + local + " (;" + ref.Variable + ";)")
		} else {
			wat.add("local.tee $" + local + " (;" + ref.Variable + ";)")
		}

		return wat, nil
	case Expression_ArrayAccess:
		panic("TODO") // TODO
	case Expression_RawMemoryReference:
		raw := lhs.Value.(RawMemoryReferenceExpression)

		localAddress := Local{Name: "", Type: Type{Type: Type_Primitive, Value: c.getEffectiveAddressType()}, IsParameter: false, Index: len(c.CurrentFunction.Locals)}
		c.CurrentFunction.Locals = append(c.CurrentFunction.Locals, localAddress)

		localValue := Local{Name: "", Type: *lhs.ValueType, IsParameter: false, Index: len(c.CurrentFunction.Locals)}
		c.CurrentFunction.Locals = append(c.CurrentFunction.Locals, localValue)

		if raw.Type.Type != Type_Primitive {
			panic("TODO") //TODO
		}

		addrWAT, err := c.compileExpressionWAT(raw.Address)
		if err != nil {
			return emptyCode(), err
		}

		wat := addrWAT

		// dup address
		wat.add(
			"local.tee $"+strconv.Itoa(localAddress.Index),
			"local.get $"+strconv.Itoa(localAddress.Index),
		)

		wat.add(c.getWATType(raw.Type) + ".load")

		if evaluateToOldValue {
			wat.add("local.tee $" + strconv.Itoa(localValue.Index))
		}

		wat.addAll(updateWAT)

		if !evaluateToOldValue {
			wat.add("local.tee $" + strconv.Itoa(localValue.Index))
		}

		wat.add(
			c.getWATType(raw.Type)+".store",
			"local.get $"+strconv.Itoa(localValue.Index),
		)

		return wat, nil
	}

	panic("assignment expr not implemented")
}

func (c *Compiler) compileExpressionWAT(expr Expression) (Code, error) {
	var err error

	switch expr.Type {
	case Expression_Assignment:
		ass := expr.Value.(AssignmentExpression)

		if ass.Operation == Operation_Nop {
			return c.compileAssignmentExpressionWAT(ass)
		}

		watRight, err := c.compileExpressionWAT(ass.Value)
		if err != nil {
			return emptyCode(), err
		}

		updateOp := c.compileOperationWAT(ass.Operation, ass.Lhs.ValueType.Value.(PrimitiveType))
		watRight.addAll(updateOp)

		return c.compileAssignmentUpdateExpressionWAT(ass.Lhs, watRight, false)
	case Expression_Literal:
		lit := expr.Value.(LiteralExpression)
		switch lit.Literal.Type {
		case Literal_Number:
			return pushConstantNumberWAT(lit.Literal.Primitive, lit.Literal.Value), nil
		case Literal_Boolean:
			if lit.Literal.Value.(bool) {
				return ofInstruction("i32.const 1"), nil
			} else {
				return ofInstruction("i32.const 0"), nil
			}
		case Literal_String:
			panic("not implemented")
		}
	case Expression_VariableReference:
		ref := expr.Value.(VariableReferenceExpression)

		cast := emptyCode()
		if expr.ValueType.Type == Type_Primitive {
			// TODO: technically only needed for function parameters because functions can be called from outside WASM so they might not be fully type checked
			cast = getTypeCast(expr.ValueType.Value.(PrimitiveType))
		}

		local := strconv.Itoa(getLocal(c.CurrentBlock, ref.Variable).Index)

		code := emptyCode()
		code.add("local.get $" + local + " (;" + ref.Variable + ";)")
		code.addAll(cast)

		return code, nil
	case Expression_Binary:
		binary := expr.Value.(BinaryExpression)

		// TODO: currently fine, only allowed for primitive types, but should be expanded to allow e.g. strings
		operandType := binary.Left.ValueType.Value.(PrimitiveType)
		exprType := expr.ValueType.Value.(PrimitiveType)

		watLeft, err := c.compileExpressionWAT(binary.Left)
		if err != nil {
			return emptyCode(), err
		}

		watRight, err := c.compileExpressionWAT(binary.Right)
		if err != nil {
			return emptyCode(), err
		}

		op := c.compileOperationWAT(binary.Operation, operandType)

		return concat(watLeft, watRight, op, getTypeCast(exprType)), nil
	case Expression_Tuple:
		tuple := expr.Value.(TupleExpression)

		wat := emptyCode()
		for _, member := range tuple.Members {
			memberWAT, err := c.compileExpressionWAT(member)
			if err != nil {
				return emptyCode(), err
			}

			wat.addAll(memberWAT)
		}

		return wat, nil
	case Expression_FunctionCall:
		fc := expr.Value.(FunctionCallExpression)

		wat := emptyCode()
		if fc.Parameters != nil {
			wat, err = c.compileExpressionWAT(*fc.Parameters)
			if err != nil {
				return emptyCode(), err
			}
		}

		switch fc.Function {
		case BUILTIN_MEMORY_GROW:
			if !c.Wasm64 {
				cast, err := castPrimitiveWAT(Primitive_U64, Primitive_U32)
				if err != nil {
					return emptyCode(), err
				}

				wat.addAll(cast)
			}

			wat.add("memory.grow")

			if !c.Wasm64 {
				cast, err := castPrimitiveWAT(Primitive_I32, Primitive_I64)
				if err != nil {
					return emptyCode(), err
				}

				wat.addAll(cast)
			}

			return wat, nil
		case BUILTIN_MEMORY_SIZE:
			wat.add("memory.size")

			if !c.Wasm64 {
				cast, err := castPrimitiveWAT(Primitive_U32, Primitive_U64)
				if err != nil {
					return emptyCode(), err
				}

				wat.addAll(cast)
			}

			return wat, nil
		default:
			wat.add("call $" + fc.Function)
			return wat, nil
		}
	case Expression_Unary:
		unary := expr.Value.(UnaryExpression)
		exprType := expr.ValueType.Value.(PrimitiveType)

		wat, err := c.compileExpressionWAT(unary.Value)
		if err != nil {
			return emptyCode(), err
		}

		watType := getPrimitiveWATType(exprType)
		switch unary.Operation {
		case UnaryOperation_Negate:
			if isFloatingPoint(exprType) {
				wat.add(watType + ".neg")
				return wat, nil
			} else {
				code := emptyCode()
				code.add(watType + ".const 0")
				code.addAll(wat)
				code.add(watType + ".sub")
				code.addAll(getTypeCast(exprType))
				return code, nil
			}
		case UnaryOperation_Nop:
			return wat, nil
		case UnaryOperation_BitwiseNot:
			if getBits(exprType) == 64 {
				wat.add(watType + ".const 0xFFFFFFFFFFFFFFFF")
			} else {
				wat.add(watType + ".const 0xFFFFFFFF")
			}

			wat.add(watType + ".xor")
			wat.addAll(getTypeCast(exprType))
			return wat, nil
		case UnaryOperation_LogicalNot:
			wat.add("i32.eqz")
			return wat, nil
		case UnaryOperation_PreIncrement, UnaryOperation_PreDecrement, UnaryOperation_PostIncrement, UnaryOperation_PostDecrement:
			valueType := c.getWATType(*unary.Value.ValueType)

			updateWAT := ofInstruction(valueType + ".const 1")
			if unary.Operation == UnaryOperation_PreIncrement || unary.Operation == UnaryOperation_PostIncrement {
				updateWAT.add(valueType + ".add")
			} else {
				updateWAT.add(valueType + ".sub")
			}

			return c.compileAssignmentUpdateExpressionWAT(unary.Value, updateWAT, unary.Operation == UnaryOperation_PostIncrement || unary.Operation == UnaryOperation_PostDecrement)
		}
	case Expression_Cast:
		cast := expr.Value.(CastExpression)

		wat, err := c.compileExpressionWAT(cast.Value)
		if err != nil {
			return emptyCode(), err
		}

		// TODO: fine, as it is currently only allowed for primitive types
		fromType := cast.Value.ValueType.Value.(PrimitiveType)
		toType := cast.Type.Value.(PrimitiveType)
		castWAT, err := castPrimitiveWAT(fromType, toType)
		if err != nil {
			return emptyCode(), err
		}

		return concat(wat, castWAT), nil
	case Expression_RawMemoryReference:
		raw := expr.Value.(RawMemoryReferenceExpression)

		wat, err := c.compileExpressionWAT(raw.Address)
		if err != nil {
			return emptyCode(), err
		}

		if raw.Type.Type == Type_Primitive {
			wat.add(c.getWATType(raw.Type) + ".load") // TODO: use load8/load16(_s/u) for smaller types
		}

		return wat, nil
	case Expression_ArrayAccess:
		array := expr.Value.(ArrayAccessExpression)

		localArray := Local{Name: "", Type: Type{Type: Type_Primitive, Value: c.getEffectiveAddressType(), Position: unknownPosition()}, IsParameter: false, Index: len(c.CurrentFunction.Locals)}
		c.CurrentFunction.Locals = append(c.CurrentFunction.Locals, localArray)

		localIndex := Local{Name: "", Type: Type{Type: Type_Primitive, Value: c.getEffectiveAddressType(), Position: unknownPosition()}, IsParameter: false, Index: len(c.CurrentFunction.Locals)}
		c.CurrentFunction.Locals = append(c.CurrentFunction.Locals, localIndex)

		arrayWAT, err := c.compileExpressionWAT(array.Array)
		if err != nil {
			return emptyCode(), err
		}

		arrayWAT.add("local.set $" + strconv.Itoa(localArray.Index) + " (;array base address;)")

		indexWAT, err := c.compileExpressionWAT(array.Index)
		if err != nil {
			return emptyCode(), err
		}

		if !c.Wasm64 {
			cast, err := castPrimitiveWAT(Primitive_I64, Primitive_I32)
			if err != nil {
				return emptyCode(), err
			}

			indexWAT.addAll(cast)
		}

		indexWAT.add("local.set $" + strconv.Itoa(localIndex.Index) + " (;array index;)")

		wat := concat(arrayWAT, indexWAT)

		if _, ok := c.CompileOptions[COMPILE_OPTION_NO_BOUNDS_CHECK]; !ok {
			// Error if index < 0
			wat.add(
				"block",
				"local.get $"+strconv.Itoa(localIndex.Index)+" (;array index;)",
				c.getAddressWATType()+".const 0",
				c.getAddressWATType()+".ge_s",
				"br_if 0",
				"call $__builtin_panic",
				"end",
			)

			// Error if index >= array length
			wat.add(
				"block",
				"local.get $"+strconv.Itoa(localIndex.Index)+" (;array index;)",
				"local.get $"+strconv.Itoa(localArray.Index)+" (;array base address;)",
				"i32.load", // Load array length
				c.getAddressWATType()+".lt_s",
				"br_if 0",
				"call $__builtin_panic",
				"end",
			)
		}

		elementType := array.Array.ValueType.Value.(ArrayType).ElementType
		wat.add(
			"local.get $"+strconv.Itoa(localIndex.Index)+" (;array index;)",
			c.getAddressWATType()+".const "+strconv.Itoa(c.getTypeSizeBytes(elementType)),
			c.getAddressWATType()+".mul",
			"local.get $"+strconv.Itoa(localArray.Index)+"(;array base address;)",
			c.getAddressWATType()+".add",
			c.getAddressWATType()+".const 4", // first 4 bytes = length
			c.getAddressWATType()+".add",
		)

		wat.add(c.getWATType(elementType) + ".load") // TODO: use load8/load16(_s/u) for smaller types

		return wat, nil
	}

	panic("expr not implemented")
}

func (c *Compiler) compileOperationWAT(operation Operation, operandType PrimitiveType) Code {
	var op string

	var suffix string
	if isUnsignedInt(operandType) {
		suffix = "u"
	} else {
		suffix = "s"
	}

	switch operation {
	case Operation_Add:
		op = getPrimitiveWATType(operandType) + ".add"
	case Operation_Sub:
		op = getPrimitiveWATType(operandType) + ".sub"
	case Operation_Mul:
		op = getPrimitiveWATType(operandType) + ".mul"
	case Operation_Div:
		op = getPrimitiveWATType(operandType) + ".div_" + suffix
	case Operation_Mod:
		op = getPrimitiveWATType(operandType) + ".rem_" + suffix
	case Operation_Greater:
		op = getPrimitiveWATType(operandType) + ".gt_" + suffix
	case Operation_Less:
		op = getPrimitiveWATType(operandType) + ".lt_" + suffix
	case Operation_GreaterEquals:
		op = getPrimitiveWATType(operandType) + ".ge_" + suffix
	case Operation_LessEquals:
		op = getPrimitiveWATType(operandType) + ".le_" + suffix
	case Operation_NotEquals:
		op = getPrimitiveWATType(operandType) + ".ne"
	case Operation_Equals:
		op = getPrimitiveWATType(operandType) + ".eq"
	default:
		panic("operation not implemented")
	}

	return ofInstruction(op)
}

func (c *Compiler) compileStatementWAT(stmt Statement, block *Block) (Code, error) {
	switch stmt.Type {
	case Statement_Expression:
		expr := stmt.Value.(ExpressionStatement)
		wat, err := c.compileExpressionWAT(expr.Expression)
		if err != nil {
			return emptyCode(), err
		}

		numItems := 0
		if expr.Expression.ValueType != nil {
			numItems = 1

			if expr.Expression.ValueType.Type == Type_Tuple {
				numItems = len(expr.Expression.ValueType.Value.(TupleType).Types)
			}
		}

		for _ = range numItems {
			wat.add("drop")
		}

		return wat, nil
	case Statement_Block:
		block := stmt.Value.(BlockStatement)
		wat, err := c.compileBlockWAT(block.Block)
		if err != nil {
			return emptyCode(), err
		}

		return wat, nil
	case Statement_Return:
		ret := stmt.Value.(ReturnStatement)

		wat := emptyCode()
		if ret.Value != nil {
			valueWAT, err := c.compileExpressionWAT(*ret.Value)
			if err != nil {
				return emptyCode(), err
			}

			wat.addAll(valueWAT)
		}

		wat.add("return")
		return wat, nil
	case Statement_DeclareLocalVariable:
		dlv := stmt.Value.(DeclareLocalVariableStatement)
		if dlv.Initializer == nil {
			return emptyCode(), nil
		}

		wat, err := c.compileExpressionWAT(*dlv.Initializer)
		if err != nil {
			return emptyCode(), err
		}

		wat.add("local.set $" + strconv.Itoa(block.Locals[dlv.Variable].Index))
		return wat, nil
	case Statement_If:
		ifS := stmt.Value.(IfStatement)

		conditionWAT, err := c.compileExpressionWAT(ifS.Condition)
		if err != nil {
			return emptyCode(), err
		}

		condBlockWAT, err := c.compileBlockWAT(ifS.ConditionalBlock)
		if err != nil {
			return emptyCode(), err
		}

		wat := emptyCode()

		if ifS.ElseBlock != nil {
			wat.add("block")
		}

		// condition
		wat.add("block")

		wat.addAll(conditionWAT)
		wat.add("i32.eqz") // logical not
		wat.add("br_if 0")

		// condition is true
		wat.addAll(condBlockWAT)

		if ifS.ElseBlock != nil {
			wat.add("br 1") // jump over else block
		}

		wat.add("end")

		if ifS.ElseBlock != nil {
			// condition is false
			elseWAT, err := c.compileBlockWAT(ifS.ElseBlock)
			if err != nil {
				return emptyCode(), err
			}

			wat.addAll(elseWAT)
			wat.add("end")
		}

		return wat, nil
	case Statement_WhileLoop:
		while := stmt.Value.(WhileLoopStatement)

		conditionWAT, err := c.compileExpressionWAT(while.Condition)
		if err != nil {
			return emptyCode(), err
		}

		bodyWAT, err := c.compileBlockWAT(while.Body)
		if err != nil {
			return emptyCode(), err
		}

		wat := emptyCode()
		wat.add("block")
		wat.add("loop")

		wat.addAll(conditionWAT)
		wat.add("i32.eqz")
		wat.add("br_if 1")

		wat.addAll(bodyWAT)
		wat.add("br 0")

		wat.add("end")
		wat.add("end")

		return wat, nil
	}

	panic("stmt not implemented")
}

func (c *Compiler) compileBlockWAT(block *Block) (Code, error) {
	blockWAT := emptyCode()

	for _, stmt := range block.Statements {
		c.CurrentBlock = block
		wat, err := c.compileStatementWAT(stmt, block)
		if err != nil {
			return emptyCode(), err
		}

		blockWAT.addAll(wat)
	}

	return blockWAT, nil
}

func (c *Compiler) compileFunctionWAT(function *ParsedFunction) (string, error) {
	c.CurrentFunction = function
	blockWat, err := c.compileBlockWAT(function.Body)
	if err != nil {
		return "", err
	}

	funcWAT := "(func $" + safeASCIIIdentifier(function.FullName) + " (export \"" + function.FullName + "\")\n"

	for _, local := range function.Locals {
		if !local.IsParameter {
			continue
		}
		funcWAT += "\t(param $" + strconv.Itoa(local.Index) + " " + c.getWATType(local.Type) + ")\n"
	}

	returnTypes := []Type{}
	if function.ReturnType != nil {
		returnTypes = []Type{*function.ReturnType}
		if function.ReturnType.Type == Type_Tuple {
			returnTypes = function.ReturnType.Value.(TupleType).Types
		}
	}

	for _, t := range returnTypes {
		funcWAT += "\t(result " + c.getWATType(t) + ")\n"
	}

	for _, local := range function.Locals {
		if local.IsParameter {
			continue
		}
		funcWAT += "\t(local $" + strconv.Itoa(local.Index) + " " + c.getWATType(local.Type) + ")\n"
	}

	return funcWAT + blockWat.toString() + ")\n", nil
}

func (c *Compiler) compile() (string, error) {
	module := "(module\n"
	module += "(memory $memory 0) (export \"memory\" (memory $memory))\n"

	module += "(func $__builtin_panic\n"
	module += "\tunreachable\n"
	module += ")\n"

	for _, file := range c.Files {
		for i := range file.Functions {
			wat, err := c.compileFunctionWAT(&file.Functions[i])
			if err != nil {
				return "", err
			}

			module += wat
		}
	}

	module += ")"
	return module, nil
}