anglais/core/compiler.go

package core

import (
	"errors"
	"fmt"
	"slices"
	"strings"
)

type Compiler struct {
	Chunk *Chunk
	ip    Pos
	scope Pos

	imports   []string
	fileStack *Stack[string]
	resolver  ImportsResolver

	source   []rune
	Warnings []CompilerError

	// optimize Whether to attempt some optimization of the emitted bytecode
	optimize bool

	stack          *Stack[LocalVariable]
	typeAliases    map[string]TypeSignature
	expectedReturn TypeSignature
}

type ImportResult struct {
	Source string
	Path   string
}

type ImportsResolver interface {
	Resolve(from, path string) (*ImportResult, error)
	IsSame(a, b string) bool
}

type LocalVariable struct {
	name      string
	signature TypeSignature
	scope     int
}

type CompilerError struct {
	Description string
	Boundary    Bounded
	Source      []rune
	Trace       []string
}

func (e CompilerError) Error() string {
	return e.Description
}

func (e CompilerError) Format() string {
	b := strings.Builder{}

	src := e.Source

	b.WriteString(e.Description)

	// highlight offending area
	start, end := e.Boundary.Bounds()

	lineEnd := 0
	lineStart := 0
	line := 1
	pos := 0

	for i := Pos(0); i <= start; i++ {
		pos++

		if src[i] == '\n' {
			line++
			lineStart = int(i) + 1
			pos = 0
		}
	}

	for lineEnd < int(end) {
		b.WriteString("\n")
		lineEnd = lineStart
		for lineEnd < len(src) {
			if src[lineEnd] == '\n' {
				lineEnd++
				break
			}

			lineEnd++
		}

		begin := max(0, int(start)-lineStart)
		length := int(min(end, Pos(lineEnd)) - max(start, Pos(lineStart)))

		lineDescriptor := fmt.Sprintf("%d:%d~%d",
			line,
			begin,
			begin+length,
		)

		b.WriteString(lineDescriptor)
		b.WriteString(" | ")

		b.WriteString(string(src[lineStart : lineEnd-1]))
		b.WriteString("\n")

		b.WriteString(strings.Repeat(" ", len(lineDescriptor)))
		b.WriteString("   ")
		b.WriteString(strings.Repeat(" ", max(int(start)-lineStart, 0)))
		b.WriteString(strings.Repeat("^", length))

		lineStart = lineEnd
		line++
	}

	b.WriteString("\nsource trace:")
	// print import stack trace
	for i, p := range slices.Backward(e.Trace) {
		b.WriteString(fmt.Sprintf("\n[%d] %s", i, p))
	}

	return b.String()
}

func NewCompiler(source []rune) *Compiler {
	c := &Compiler{
		NewChunk(make([]Bytecode, 0), make([]Value, 0)),
		0,
		0,
		make([]string, 0),
		NewStack[string](256),
		nil,
		source,
		[]CompilerError{},
		false,
		NewStack[LocalVariable](256),
		map[string]TypeSignature{},
		nil,
	}

	return c
}

func (c *Compiler) add(instruction Bytecode) {
	for len(c.Chunk.Bytecode) <= int(c.ip) {
		c.Chunk.Bytecode = append(c.Chunk.Bytecode, 0)
	}

	c.Chunk.Bytecode[c.ip] = instruction

	c.advance(1)
}

// addConstant add both a constant (if it is not already defined), and add the index of it to the bytecode
func (c *Compiler) addConstant(value Value) {
	chunk := c.Chunk
	for i := 0; i < len(chunk.Constants); i++ {
		if chunk.Constants[i].Equals(value) {
			c.add(Bytecode(i))

			return
		}
	}

	chunk.Constants = append(chunk.Constants, value)

	if len(chunk.Constants) > 256 {
		panic("too many constants (>256)")
	}

	c.add(Bytecode(len(chunk.Constants) - 1))
}

func (c *Compiler) Compile(p *Program) (TypeSignature, error) {
	c.fileStack.Push(p.Path)

	return c.compile(p.Block)
}

func EscapeString(in string) string {
	var out strings.Builder
	escaped := false

	for _, ch := range in {
		if escaped {
			switch ch {
			case 'n':
				out.WriteRune('\n')
			case 't':
				out.WriteRune('\t')
			case 'r':
				out.WriteRune('\r')
			default:
				out.WriteString(string(ch))
			}
			escaped = false
			continue
		}

		switch ch {
		case '\\':
			escaped = true
		default:
			out.WriteString(string(ch))
		}
	}

	return out.String()
}

func (c *Compiler) resolveType(value TypeSignature) TypeSignature {
	if value.Type() == TypeNamed {
		return c.typeAliases[value.(*NamedSignature).Name]
	}

	return value
}

func (c *Compiler) typeMatches(value, template TypeSignature) bool {
	value = c.resolveType(value)
	template = c.resolveType(template)

	return template.Contains(value)
}

func (c *Compiler) compile(tree Node) (TypeSignature, error) {
	if tree == nil {
		panic("compile called with nil value")
	}

	switch tree.Type() {
	case StringNodeType:
		c.add(InstructionConstant)
		c.addConstant(&StringValue{
			EscapeString(tree.(*StringNode).value),
		})
		return &StringSignature{}, nil

	case FloatNodeType:
		c.add(InstructionConstant)
		c.addConstant(&FloatValue{tree.(*FloatNode).value})
		return &FloatSignature{}, nil

	case IntegerNodeType:
		c.add(InstructionConstant)
		c.addConstant(&IntegerValue{tree.(*IntegerNode).value})
		return &IntegerSignature{}, nil

	case TupleNodeType:
		n := tree.(*TupleNode)

		var contents []TypeSignature
		for _, n := range n.items {
			t, err := c.compile(n)
			if err != nil {
				return nil, err
			}

			contents = append(contents, t)
		}
		c.add(InstructionFormTuple)
		c.addU16(uint16(len(n.items)))

		return &TupleSignature{contents}, nil

	case RecordNodeType:
		n := tree.(*RecordNode)

		c.add(InstructionNewRecord)

		contents := map[string]TypeSignature{}
		for k, v := range n.entries {
			t, err := c.compile(v)
			if err != nil {
				return nil, err
			}

			c.add(InstructionSetRecordItem)
			c.addConstant(&StringValue{
				k,
			})

			contents[k] = t
		}

		return &RecordSignature{
			contents,
		}, nil

	case ListNodeType:
		l := tree.(*ListNode)

		contents := l.content

		for _, n := range l.items {
			t, err := c.compile(n)
			if err != nil {
				return nil, err
			}

			if contents == nil {
				contents = t
			} else if !c.typeMatches(t, contents) {
				contents = &CompositeSignature{
					contents,
					t,
				}
			}
		}

		c.add(InstructionFormList)
		c.addU16(uint16(len(l.items)))

		return &ListSignature{contents}, nil

	case ReferenceNodeType:
		return c.addGetVar(tree.(*ReferenceNode).name, tree)

	case BinaryNodeType:
		return c.compileBinary(tree.(*BinaryNode))

	case UnaryNodeType:
		vt, err := c.compile(tree.(*UnaryNode).value)
		if err != nil {
			return nil, err
		}

		switch tree.(*UnaryNode).UnaryOperation {
		case UnaryNegate:
			if vt.Type() == TypeInteger {
				c.add(InstructionNegateInt)
			} else {
				c.add(InstructionNegateFloat)
			}

			return vt, nil

		case UnaryNot:
			c.add(InstructionNot)
			return &BooleanSignature{}, nil
		}

		return nil, c.error("unimplemented unary operation", tree.(*UnaryNode).operator)

	case BooleanNodeType:
		if tree.(*BooleanNode).Boolean {
			c.add(InstructionTrue)
		} else {
			c.add(InstructionFalse)
		}
		return &BooleanSignature{}, nil

	case NilNodeType:
		c.add(InstructionNil)
		return &NilSignature{}, nil

	case BlockNodeType:
		if len(tree.(*BlockNode).statements) == 0 {
			c.add(InstructionNil)
			return &NilSignature{}, nil
		}

		c.addDescend()
		var last TypeSignature
		var err error
		for i, n := range tree.(*BlockNode).statements {
			last, err = c.compile(n)
			if err != nil {
				return nil, err
			}

			if i != len(tree.(*BlockNode).statements)-1 {
				c.add(InstructionPop)
			}
		}
		c.addAscend()

		return last, nil

	case ConditionalNodeType:
		n := tree.(*ConditionalNode)

		if v, ok := n.condition.(*BooleanNode); ok {
			if v.Boolean {
				c.warn("condition is always true", n.condition)
				return c.compile(n.do)
			}

			c.warn("condition is always false", n.condition)
			if n.otherwise != nil {
				return c.compile(n.otherwise)
			}

			c.add(InstructionNil)
			return &NilSignature{}, nil
		}

		// the stack should have whether the condition was truthful
		sig, err := c.compile(n.condition)
		if err != nil {
			return nil, err
		}

		// make sure condition is boolean
		if sig.Type() != TypeBoolean {
			return nil, c.error(fmt.Sprintf("condition must be boolean (is non-boolean type %s)", sig), n.condition)
		}

		// if the condition equated to true, we should jump over the body
		c.add(InstructionJumpFalse)
		// we save where uint16 jump by value is stored, and update it when
		// we know the size of this condition (in bytecode)
		jumpByPos := c.ip
		c.advance(2)

		// this part would be executed if the value was true
		dot, err := c.compile(n.do)
		if err != nil {
			return nil, err
		}

		// we store the position of the jump over the else code here
		// this would jump over the else/otherwise block in the code
		c.add(InstructionJump)
		jumpOverElse := c.ip
		c.advance(2)

		// put the u16 of where to jump if the condition was false
		c.putU16(jumpByPos, uint16(c.ip-jumpByPos-2))

		var ot TypeSignature
		if n.otherwise != nil {
			ot, err = c.compile(n.otherwise)
			if err != nil {
				return nil, err
			}
		} else {
			c.add(InstructionNil)
			ot = &NilSignature{}
		}

		c.putU16(jumpOverElse, uint16(c.ip-jumpOverElse-2))

		if dot.Contains(ot) {
			return dot, nil
		} else if ot.Contains(dot) {
			return ot, nil
		}

		return &CompositeSignature{
			dot,
			ot,
		}, nil

	case LoopNodeType:
		n := tree.(*LoopNode)

		c.add(InstructionNil)

		conditionPos := c.ip
		jumpValuePos := Pos(0)

		alwaysLoop := false
		if v, ok := n.condition.(*BooleanNode); ok {
			if !v.Boolean {
				c.warn("while-loop condition is always false", n.condition)
				return &NilSignature{}, nil
			}

			c.warn("while-loop condition is always true", n.condition)
			alwaysLoop = true
		} else {
			sig, err := c.compile(n.condition)
			if err != nil {
				return nil, err
			}

			// make sure condition is boolean
			if sig.Type() != TypeBoolean {
				return nil, c.error(fmt.Sprintf("cannot loop depending on value of type %s; requires boolean", sig), n.condition)
			}

			c.add(InstructionJumpFalse)
			jumpValuePos = c.ip
			c.advance(2)
		}

		c.add(InstructionPop)

		dt, err := c.compile(n.do)
		if err != nil {
			return nil, err
		}

		c.add(InstructionLoop)
		// condition pos < ip
		c.addU16(uint16(c.ip - conditionPos + 2))

		if !alwaysLoop {
			c.putU16(jumpValuePos, uint16(c.ip-jumpValuePos-2))
		}

		return &CompositeSignature{dt, &NilSignature{}}, nil

	case ForNodeType:
		n := tree.(*ForNode)

		is, err := c.compile(n.iterator)
		if err != nil {
			return nil, err
		}

		iteratorSignature := &FunctionSignature{
			[]TypeSignature{},
			&TupleSignature{
				[]TypeSignature{
					&AnySignature{},
					&BooleanSignature{},
				},
			},
		}

		if !iteratorSignature.Contains(is) {
			return nil, c.error(fmt.Sprintf("cannot iterate with non-iterator %s (must be %s)", is, iteratorSignature), n.iterator)
		}

		outputSig := is.(*FunctionSignature).Out.(*TupleSignature).Contents[0]
		ipos := c.ip

		c.addDescend()
		c.add(InstructionDuplicate)
		c.add(InstructionCall)
		c.add(InstructionDestructureTuple)

		// if no more items; jump to end
		c.add(InstructionJumpFalse)
		jmpValuePos := c.ip
		c.advance(2)

		if n.counter.Type() != ReferenceNodeType {
			return nil, c.error("cannot use non-variable as a counter", n.counter)
		}

		name := n.counter.(*ReferenceNode).name

		c.add(InstructionDeclareLocal)
		c.addConstant(&StringValue{
			name,
		})
		c.add(InstructionPop)
		c.registerVar(name, outputSig)

		_, err = c.compile(n.logic)
		if err != nil {
			return nil, err
		}
		c.add(InstructionPop)

		c.addAscend()

		c.add(InstructionLoop)
		c.addU16(uint16(c.ip - ipos + 2))

		// end of loop
		c.putU16(jmpValuePos, uint16(c.ip-jmpValuePos-2))

		c.add(InstructionPop)
		c.add(InstructionPop)
		c.add(InstructionNil)

		return &NilSignature{}, nil

	case AssignNodeType:
		n := tree.(*AssignNode)

		t, err := c.compile(n.value)
		if err != nil {
			return nil, err
		}

		return c.compileAssignFromStack(n.dest, t, n.declare)

	case InvokeNodeType:
		n := tree.(*InvokeNode)

		var argSigs []TypeSignature
		var err error
		for _, arg := range n.args {
			sig, err := c.compile(arg)
			if err != nil {
				return nil, err
			}
			argSigs = append(argSigs, sig)
		}

		s, err := c.compile(n.source)
		if err != nil {
			return nil, err
		}

		f, ok := s.(*FunctionSignature)
		if !ok {
			return nil, c.error(fmt.Sprintf("cannot call non-function value of type %s", s), n)
		}

		if len(n.args) != len(f.In) {
			return nil, c.error(fmt.Sprintf("wrong argument count: function of signature %s got %d, requires %d", f, len(n.args), len(f.In)), n)
		}

		for i, sig := range argSigs {
			// check that arg type is as required
			fin := f.In[i]
			if !c.typeMatches(sig, fin) {
				return nil, c.error(fmt.Sprintf("argument #%d does not have expected type signature: got %s, requires %s", i, sig, f.In[i]), n.args[i])
			}
		}

		c.add(InstructionCall)
		return f.Out, nil

	case FunctionNodeType:
		n := tree.(*FunctionNode)

		fi := len(c.Chunk.Constants)
		c.Chunk.Constants = append(c.Chunk.Constants, nil)

		c.add(InstructionConstant)
		c.add(Bytecode(fi))

		// allow self-referencing
		sig := n.Signature()
		c.descend()
		c.registerVar(n.name, sig)

		// keep track of main chunk
		mc := c.Chunk
		// and ip
		mip := c.ip

		// assign a new empty chunk
		c.Chunk = NewChunk(make([]Bytecode, 0), make([]Value, 0))
		// reset instruction pointer (ip)
		c.ip = 0

		c.descend()
		for _, p := range n.parameters {
			c.registerVar(p.Name, p.Signature)
		}

		parentExpectedReturn := c.expectedReturn
		c.expectedReturn = sig.Out

		yield, err := c.compile(n.logic)
		if err != nil {
			return nil, err
		}

		if c.expectedReturn.Type() == TypeNil && yield.Type() != TypeNil {
			c.add(InstructionPop)
			c.add(InstructionNil)
		} else if !c.typeMatches(yield, c.expectedReturn) {
			var causer Node = n
			if v, ok := n.logic.(*BlockNode); ok && len(v.statements) > 0 {
				causer = v.statements[len(v.statements)-1]
			}

			return nil, c.error(fmt.Sprintf("yield does not match expected return; got %s, expected %s", yield, c.expectedReturn), causer)
		}

		c.ascend()
		c.ascend()

		mc.Constants[fi] = &FunctionValue{
			n.name,
			n.parameters,
			n.yield,
			c.Chunk,
			nil,
			nil,
		}

		// restore old chunk and ip
		c.Chunk = mc
		c.ip = mip
		c.expectedReturn = parentExpectedReturn

		return sig, nil

	case IncludeNodeType:
		return c.compileInclude(tree.(*IncludeNode))

	case AccessNodeType:
		n := tree.(*AccessNode)
		ps, err := c.compile(n.source)
		if err != nil {
			return nil, err
		}
		c.add(InstructionAccessProperty)
		c.addConstant(&StringValue{
			n.property.Lexeme,
		})

		s, err := c.getPropertySignature(ps, n.property.Lexeme)
		if err != nil {
			return nil, c.error(err.Error(), n.property)
		}

		return s, nil

	case ReturnNodeType:
		if c.expectedReturn == nil {
			return nil, c.error("cannot return", tree)
		}

		t, err := c.compile(tree.(*ReturnNode).value)
		if err != nil {
			return nil, err
		}

		if !c.typeMatches(t, c.expectedReturn) {
			return nil, c.error(fmt.Sprintf("cannot return %s; must be %s", t, c.expectedReturn), tree.(*ReturnNode).value)
		}

		c.add(InstructionReturn)
		return t, nil

	case AliasNodeType:
		n := tree.(*AliasNode)

		if _, ok := c.typeAliases[n.name.Lexeme]; ok {
			return nil, c.error(fmt.Sprintf("%s is already a declared type alias", n.name.Lexeme), n.name)
		}

		c.typeAliases[n.name.Lexeme] = n.signature
		c.add(InstructionNil)

		return &NilSignature{}, nil

	case IndexNodeType:
		n := tree.(*IndexNode)

		st, err := c.compile(n.source)
		if err != nil {
			return nil, err
		}

		st = c.resolveType(st)

		it, err := c.compile(n.index)
		if err != nil {
			return nil, err
		}

		if it.Type() != TypeInteger {
			return nil, c.error(fmt.Sprintf("can only index with integers (got %s, nice try)", it), n.index)
		}

		var output TypeSignature
		switch st.Type() {
		case TypeList:
			// list stuff
			output = st.(*ListSignature).Contents
			c.add(InstructionIndexList)
		case TypeTuple:
			// Tuple stuff
			sig := st.(*TupleSignature)
			if len(sig.Contents) == 0 {
				return nil, c.error("cannot index into empty tuple", n.source)
			}

			if n.index.Type() == IntegerNodeType {
				in := n.index.(*IntegerNode)

				i := in.value.Int64()
				if i < 0 || int64(len(sig.Contents)) <= i {
					return nil, c.error(fmt.Sprintf("cannot index outside of tuple (%d items)", len(sig.Contents)), n.source)
				}

				output = sig.Contents[i]
			} else {
				output = sig.Contents[0]
				for _, is := range sig.Contents[1:] {
					if c.typeMatches(is, output) {
						continue
					}

					output = &CompositeSignature{
						output,
						is,
					}
				}
			}

			c.add(InstructionIndexTuple)
		case TypeString:
			output = &StringSignature{}
			c.add(InstructionIndexString)
		default:
			return nil, c.error(fmt.Sprintf("cannot index into value of type %s", st), n.source)
		}

		return output, nil

	case BreakpointNodeType:
		c.add(InstructionBreakpoint)

		c.add(InstructionNil)
		return &NilSignature{}, nil

	default:
		panic(fmt.Sprintf("unimplemented compiling of %s", tree.Type()))
	}
}

func (c *Compiler) compileBinary(binary *BinaryNode) (TypeSignature, error) {
	tl, err := c.compile(binary.Left)
	if err != nil {
		return nil, err
	}
	tr, err := c.compile(binary.Right)
	if err != nil {
		return nil, err
	}

	if tl.Type() != tr.Type() {
		return nil, c.error(fmt.Sprintf("cannot %s values of different types (%s and %s)", binary.BinaryOperation, tl, tr), binary.operator)
	}

	res := tl
	switch binary.BinaryOperation {
	case BinaryAddition:
		if tl.Type() == TypeString {
			c.add(InstructionConcatStrings)
		} else if tl.Type() == TypeList {
			c.add(InstructionConcatLists)
		} else if tl.Type() == TypeFloat {
			c.add(InstructionAddFloat)
		} else if tl.Type() == TypeInteger {
			c.add(InstructionAddInt)
		} else {
			return nil, c.error("unimplemented binary compilation", binary)
		}

	case BinarySubtraction:
		if tl.Type() == TypeFloat {
			c.add(InstructionSubFloat)
		} else if tl.Type() == TypeInteger {
			c.add(InstructionSubInt)
		} else {
			return nil, c.error(fmt.Sprintf("cannot subtract %s", tl), binary.operator)
		}
	case BinaryMultiplication:
		if tl.Type() == TypeFloat {
			c.add(InstructionMulFloat)
		} else if tl.Type() == TypeInteger {
			c.add(InstructionMulInt)
		} else {
			return nil, c.error(fmt.Sprintf("cannot multiply %s", tl), binary.operator)
		}
	case BinaryDivision:
		if tl.Type() == TypeFloat {
			c.add(InstructionDivFloat)
		} else if tl.Type() == TypeInteger {
			c.add(InstructionDivInt)
		} else {
			return nil, c.error(fmt.Sprintf("cannot divide %s", tl), binary.operator)
		}

	case BinaryModulo:
		if tl.Type() == TypeInteger {
			c.add(InstructionModInt)
		} else {
			return nil, c.error(fmt.Sprintf("cannot compute modulo of %s", tl), binary.operator)
		}
	case BinaryEquality:
		c.add(InstructionEquals)
		res = &BooleanSignature{}
	case BinaryInequality:
		c.add(InstructionNotEqual)
		res = &BooleanSignature{}

	case BinaryLess:
		if tl.Type() == TypeFloat {
			c.add(InstructionLessFloat)
		} else if tl.Type() == TypeInteger {
			c.add(InstructionLessInt)
		} else {
			return nil, c.error(fmt.Sprintf("cannot compare ordering of %s", tl), binary.operator)
		}
		res = &BooleanSignature{}
	case BinaryGreater:
		if tl.Type() == TypeFloat {
			c.add(InstructionGreaterFloat)
		} else if tl.Type() == TypeInteger {
			c.add(InstructionGreaterInt)
		} else {
			return nil, c.error(fmt.Sprintf("cannot compare ordering of %s", tl), binary.operator)
		}
		res = &BooleanSignature{}
	case BinaryLessEqual:
		if tl.Type() == TypeFloat {
			c.add(InstructionLessOrEqualFloat)
		} else if tl.Type() == TypeInteger {
			c.add(InstructionLessOrEqualInt)
		} else {
			return nil, c.error(fmt.Sprintf("cannot compare ordering of %s", tl), binary.operator)
		}
		res = &BooleanSignature{}
	case BinaryGreaterEqual:
		if tl.Type() == TypeFloat {
			c.add(InstructionGreaterOrEqualFloat)
		} else if tl.Type() == TypeInteger {
			c.add(InstructionGreaterOrEqualInt)
		} else {
			return nil, c.error(fmt.Sprintf("cannot compare ordering of %s", tl), binary.operator)
		}
		res = &BooleanSignature{}

	case BinaryBooleanAnd:
		if tl.Type() != TypeBoolean {
			return nil, c.error(fmt.Sprintf("cannot boolean-and of non-boolean %s", tl), binary.operator)
		}

		c.add(InstructionAnd)
		res = &BooleanSignature{}
	case BinaryBooleanOr:
		if tl.Type() != TypeBoolean {
			return nil, c.error(fmt.Sprintf("cannot boolean-or of non-boolean %s", tl), binary.operator)
		}

		c.add(InstructionOr)
		res = &BooleanSignature{}
	}

	return res, nil
}

// compileAssignFromStack assign the value of type sig which is expected to be on top of the stack.
func (c *Compiler) compileAssignFromStack(to Node, sig TypeSignature, declare bool) (TypeSignature, error) {
	switch to.Type() {
	case ReferenceNodeType:
		d := to.(*ReferenceNode)

		if d.name == "_" {
			return sig, nil
		}

		if declare && c.isVarDeclaredHere(d.name) {
			return nil, c.error(fmt.Sprintf("%s is already declared in this scope", d.name), to)
		}

		return c.addSetVar(d.name, sig, declare, to)
	case TupleNodeType:
		t := to.(*TupleNode)

		tsig, ok := sig.(*TupleSignature)
		if !ok {
			return nil, c.error(fmt.Sprintf("cannot destructure non-tuple %s", sig), to)
		}

		if len(t.items) != len(tsig.Contents) {
			return nil, c.error(fmt.Sprintf("not same amount of items; must be %d", len(tsig.Contents)), to)
		}

		c.add(InstructionDuplicate)
		c.add(InstructionDestructureTuple)

		// iterate from top to bottom
		for i, v := range slices.Backward(t.items) {
			_, err := c.compileAssignFromStack(v, tsig.Contents[i], declare)
			if err != nil {
				return nil, err
			}
			c.add(InstructionPop)
		}

		return sig, nil
	case IndexNodeType:
		if declare {
			return nil, c.error(fmt.Sprintf("cannot declare an indexed item"), to)
		}

		n := to.(*IndexNode)

		ssig, err := c.compile(n.source)
		if err != nil {
			return nil, err
		}

		isig, err := c.compile(n.index)
		if err != nil {
			return nil, err
		}

		if isig.Type() != TypeInteger {
			return nil, c.error(fmt.Sprintf("cannot index into list with non-integer (%s)", isig), n.index)
		}

		switch ssig.Type() {
		case TypeList:
			lsig := ssig.(*ListSignature)
			if !c.typeMatches(sig, lsig.Contents) {
				return nil, c.error(fmt.Sprintf("cannot assign value of type %s to list with items of type %s", sig, lsig.Contents), to)
			}

			c.add(InstructionSetIndexList)
		default:
			return nil, c.error(fmt.Sprintf("cannot set index of %s", ssig.Type()), n.source)
		}

		return sig, nil

	default:
		return nil, c.error(fmt.Sprintf("cannot assign to %s", to.Type()), to)
	}
}

func (c *Compiler) getVarSignature(name string, causer Node) (TypeSignature, error) {
	if c.isGlobal(name) {
		return SignatureOf(DefaultGlobals[name]), nil
	}

	for i := c.stack.Current - 1; i >= 0; i-- {
		v := c.stack.items[i]
		if v.name == name {
			return v.signature, nil
		}
	}

	return nil, c.error(fmt.Sprintf("variable %s not defined", name), causer)
}

// isVarDeclaredHere check whether a variable is declared in the current scope
func (c *Compiler) isVarDeclaredHere(name string) bool {
	for i := c.stack.Current - 1; i >= 0 && c.stack.items[i].scope == int(c.scope); i-- {
		v := c.stack.items[i]
		if v.name == name {
			return true
		}
	}

	return false
}

func (c *Compiler) addGetVar(name string, causer Node) (TypeSignature, error) {
	if c.isGlobal(name) {
		c.add(InstructionGetGlobal)
		c.addConstant(&StringValue{
			name,
		})
	} else {
		c.add(InstructionGetLocal)
		c.addConstant(&StringValue{
			name,
		})
	}

	return c.getVarSignature(name, causer)
}

// addSetVar add instructions for setting a variable of specified type which is ON TOP OF THE STACK
// does also register the variable with the correct type.
func (c *Compiler) addSetVar(name string, t TypeSignature, declare bool, causer Node) (TypeSignature, error) {
	if declare {
		c.add(InstructionDeclareLocal)
		c.registerVar(name, t)
	} else {
		vt, err := c.getVarSignature(name, causer) // it needs someone to blame >:3
		if err != nil {
			return nil, err
		}

		if !vt.Contains(t) {
			return nil, c.error(fmt.Sprintf("cannot assign value of type %s to variable %s of type %s", t, name, vt), causer)
		}

		c.add(InstructionSetLocal)
	}

	c.addConstant(&StringValue{
		name,
	})

	return t, nil
}

// keep track that a variable is declared but doesn't necessarily have a deducible type
func (c *Compiler) registerVar(name string, t TypeSignature) {
	c.stack.Push(LocalVariable{
		name,
		t,
		int(c.scope),
	})
}

// isLocal whether a variable of with the name provided is declared within the local scope
func (c *Compiler) isLocal(name string) bool {
	for i := c.stack.Current - 1; i >= 0; i-- {
		if c.stack.items[i].name == name {
			return true
		}
	}
	return false
}

// isGlobal whether a variable is defined in the standard global environment
func (c *Compiler) isGlobal(name string) bool {
	return DefaultGlobals[name] != nil
}

func (c *Compiler) ascend() {
	c.scope--

	for ; c.stack.Current > 0 && c.stack.Peek().scope > int(c.scope); c.stack.Pop() {
	}
}

func (c *Compiler) addAscend() {
	c.ascend()
	c.add(InstructionAscend)
}

func (c *Compiler) descend() {
	c.scope++
}

func (c *Compiler) addDescend() {
	c.descend()
	c.add(InstructionDescend)
}

func (c *Compiler) error(msg string, causer Bounded) CompilerError {
	return CompilerError{
		msg,
		causer,
		c.source,
		c.fileStack.Slice(),
	}
}

func (c *Compiler) warn(msg string, causer Node) {
	c.Warnings = append(c.Warnings, c.error(msg, causer))
}

func (c *Compiler) compileInclude(include *IncludeNode) (TypeSignature, error) {
	res, err := c.resolver.Resolve(c.fileStack.Peek(), include.path.value)
	if err != nil {
		return nil, err
	}

	// warn if already included
	for _, i := range c.imports {
		if c.resolver.IsSame(res.Path, i) {
			c.warn("already included elsewhere", include)
		}
	}

	// stop recursive includes
	for i := c.fileStack.Current - 1; i >= 0; i-- {
		if c.resolver.IsSame(res.Path, c.fileStack.items[i]) {
			return nil, c.error("recursive inclusion", include)
		}
	}

	l := NewLexer(res.Source)
	tokens, err := l.Tokenize()
	if err != nil {
		return nil, err
	}

	parser := NewParser(res.Source, append(c.fileStack.Slice(), res.Path), tokens)
	p, err := parser.Parse(res.Path)
	if err != nil {
		return nil, err
	}

	oldSrc := c.source

	// update source for more descriptive errors
	c.source = []rune(res.Source)
	t, err := c.Compile(p)
	if err != nil {
		return nil, err
	}

	c.source = oldSrc

	return t, nil
}

func (c *Compiler) SetImportsResolver(resolver ImportsResolver) {
	c.resolver = resolver
}

func (c *Compiler) SetSource(src string) {
	c.source = []rune(src)
}

func (c *Compiler) advance(amount Pos) {
	c.ip += amount
}

func (c *Compiler) addU16(v uint16) {
	c.add(Bytecode(v >> 8))   // first 8 bits
	c.add(Bytecode(v & 0xff)) // last 8 bits
}

// putU16 put an unsigned 16-bit value at an arbitrary position.
// p is the position before the value
func (c *Compiler) putU16(p Pos, v uint16) {
	// save original position
	start := c.ip

	// move to position
	c.ip = p
	// set values of the next 2 bytes to the u16
	c.addU16(v)

	// restore position
	c.ip = start
}

var TypePrototypes = map[Type]*map[string]*BuiltinFunctionValue{
	TypeString: &StringPrototype,
	TypeTuple:  &TuplePrototype,
	TypeList:   &ListPrototype,
	TypeObject: &ObjectPrototype,
}

func (c *Compiler) getPropertySignature(source TypeSignature, property string) (TypeSignature, error) {
	sig := c.resolveType(source)

	switch sig.Type() {
	case TypeAny:
		return nil, errors.New("cannot deduce properties of type any")
	case TypeComposite:
		csig := sig.(*CompositeSignature)

		at, err := c.getPropertySignature(csig.A, property)
		if err != nil {
			return nil, err
		}

		bt, err := c.getPropertySignature(csig.B, property)
		if err != nil {
			return nil, err
		}

		if at.Equal(bt) {
			return at, nil
		}

		return &CompositeSignature{
			at, bt,
		}, nil
	case TypeRecord:
		prop, ok := sig.(*RecordSignature).Entries[property]
		if !ok {
			return nil, errors.New(fmt.Sprintf("cannot record has no property \"%s\"", property))
		}

		return prop, nil
	default:
	}

	if prot, pOk := TypePrototypes[sig.Type()]; pOk {
		v, ok := (*prot)[property]
		if !ok {
			return nil, errors.New(fmt.Sprintf("list has no property %s", property))
		}

		return SignatureOf(v), nil
	}

	return nil, errors.New(fmt.Sprintf("%s has no properties", sig.Type()))
}