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builtin_special.go
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/
builtin_special.go
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package eval
// Builtin special forms. Special forms behave mostly like ordinary commands -
// they are valid commands syntactically, and can take part in pipelines - but
// they have special rules for the evaluation of their arguments and can affect
// the compilation phase (whereas ordinary commands can only affect the
// evaluation phase).
//
// For instance, the "and" special form evaluates its arguments from left to
// right, and stops as soon as one booleanly false value is obtained: the
// command "and $false (fail haha)" does not produce an exception.
//
// As another instance, the "del" special form removes a variable, affecting the
// compiler.
//
// Flow control structures are also implemented as special forms in elvish, with
// closures functioning as code blocks.
import (
"os"
"path/filepath"
"strings"
"github.com/elves/elvish/pkg/diag"
"github.com/elves/elvish/pkg/eval/vals"
"github.com/elves/elvish/pkg/eval/vars"
"github.com/elves/elvish/pkg/parse"
)
type compileBuiltin func(*compiler, *parse.Form) effectOpBody
var builtinSpecials map[string]compileBuiltin
// IsBuiltinSpecial is the set of all names of builtin special forms. It is
// intended for external consumption, e.g. the syntax highlighter.
var IsBuiltinSpecial = map[string]bool{}
type noSuchModule struct{ spec string }
func (err noSuchModule) Error() string { return "no such module: " + err.spec }
func init() {
// Needed to avoid initialization loop
builtinSpecials = map[string]compileBuiltin{
"del": compileDel,
"fn": compileFn,
"use": compileUse,
"and": compileAnd,
"or": compileOr,
"if": compileIf,
"while": compileWhile,
"for": compileFor,
"try": compileTry,
}
for name := range builtinSpecials {
IsBuiltinSpecial[name] = true
}
}
const delArgMsg = "arguments to del must be variable or variable elements"
// DelForm = 'del' { VariablePrimary }
func compileDel(cp *compiler, fn *parse.Form) effectOpBody {
var ops []effectOp
for _, cn := range fn.Args {
if len(cn.Indexings) != 1 {
cp.errorpf(cn, delArgMsg)
continue
}
head, indicies := cn.Indexings[0].Head, cn.Indexings[0].Indicies
if head.Type != parse.Bareword {
if head.Type == parse.Variable {
cp.errorpf(cn, "arguments to del must drop $")
} else {
cp.errorpf(cn, delArgMsg)
}
continue
}
sigil, qname := SplitVariableRef(head.Value)
if sigil != "" {
cp.errorpf(cn, "arguments to del may not have a sigils, got %q", sigil)
continue
}
var f effectOpBody
if len(indicies) == 0 {
ns, name := SplitQNameNsFirst(qname)
switch ns {
case "", ":", "local:":
if !cp.thisScope().has(name) {
cp.errorpf(cn, "no variable $%s in local scope", name)
continue
}
cp.thisScope().del(name)
f = delLocalVarOp{name}
case "E:":
f = delEnvVarOp{name}
default:
cp.errorpf(cn, "only variables in local: or E: can be deleted")
continue
}
} else {
if !cp.registerVariableGet(qname, nil) {
cp.errorpf(cn, "no variable $%s", head.Value)
continue
}
f = newDelElementOp(qname, head.Range().From, head.Range().To, cp.arrayOps(indicies))
}
ops = append(ops, effectOp{f, cn.Range()})
}
return seqOp{ops}
}
type delLocalVarOp struct{ name string }
func (op delLocalVarOp) invoke(fm *Frame) error {
delete(fm.local, op.name)
return nil
}
type delEnvVarOp struct{ name string }
func (op delEnvVarOp) invoke(*Frame) error {
return os.Unsetenv(op.name)
}
func newDelElementOp(qname string, begin, headEnd int, indexOps []valuesOp) effectOpBody {
ends := make([]int, len(indexOps)+1)
ends[0] = headEnd
for i, op := range indexOps {
ends[i+1] = op.To
}
return &delElemOp{qname, indexOps, begin, ends}
}
type delElemOp struct {
qname string
indexOps []valuesOp
begin int
ends []int
}
func (op *delElemOp) invoke(fm *Frame) error {
var indicies []interface{}
for _, indexOp := range op.indexOps {
indexValues, err := indexOp.exec(fm)
if err != nil {
return err
}
if len(indexValues) != 1 {
return fm.errorpf(indexOp, "index must evaluate to a single value in argument to del")
}
indicies = append(indicies, indexValues[0])
}
err := vars.DelElement(fm.ResolveVar(op.qname), indicies)
if err != nil {
if level := vars.ElementErrorLevel(err); level >= 0 {
return fm.errorp(diag.Ranging{From: op.begin, To: op.ends[level]}, err)
}
return err
}
return nil
}
// FnForm = 'fn' StringPrimary LambdaPrimary
//
// fn f []{foobar} is a shorthand for set '&'f = []{foobar}.
func compileFn(cp *compiler, fn *parse.Form) effectOpBody {
args := cp.walkArgs(fn)
nameNode := args.next()
varName := mustString(cp, nameNode, "must be a literal string") + FnSuffix
bodyNode := args.nextMustLambda()
args.mustEnd()
cp.registerVariableSet(":" + varName)
op := cp.lambda(bodyNode)
return fnOp{varName, op}
}
type fnOp struct {
varName string
lambdaOp valuesOpBody
}
func (op fnOp) invoke(fm *Frame) error {
// Initialize the function variable with the builtin nop function. This step
// allows the definition of recursive functions; the actual function will
// never be called.
fm.local[op.varName] = vars.FromInit(NewGoFn("<shouldn't be called>", nop))
values, err := op.lambdaOp.invoke(fm)
if err != nil {
return err
}
closure := values[0].(*Closure)
closure.Op = wrapFn(closure.Op)
return fm.local[op.varName].Set(closure)
}
func wrapFn(op effectOp) effectOp {
return effectOp{fnWrap{op}, op.Ranging}
}
type fnWrap struct{ wrapped effectOp }
func (op fnWrap) invoke(fm *Frame) error {
err := op.wrapped.exec(fm)
if err != nil && Cause(err) != Return {
// rethrow
return err
}
return nil
}
// UseForm = 'use' StringPrimary
func compileUse(cp *compiler, fn *parse.Form) effectOpBody {
var name, spec string
switch len(fn.Args) {
case 0:
end := fn.Head.Range().To
cp.errorpf(diag.PointRanging(end), "lack module name")
case 1:
spec = mustString(cp, fn.Args[0],
"module spec should be a literal string")
// Use the last path component as the name; for instance, if path =
// "a/b/c/d", name is "d". If path doesn't have slashes, name = path.
name = spec[strings.LastIndexByte(spec, '/')+1:]
case 2:
// TODO(xiaq): Allow using variable as module path
spec = mustString(cp, fn.Args[0],
"module spec should be a literal string")
name = mustString(cp, fn.Args[1],
"module name should be a literal string")
default: // > 2
cp.errorpf(diag.MixedRanging(fn.Args[2], fn.Args[len(fn.Args)-1]),
"superfluous argument(s)")
}
cp.thisScope().set(name + NsSuffix)
return useOp{fn.Range(), name, spec}
}
type useOp struct {
diag.Ranging
name, spec string
}
func (op useOp) invoke(fm *Frame) error {
ns, err := loadModule(fm, op, op.spec)
if err != nil {
return err
}
fm.local.AddNs(op.name, ns)
return nil
}
func loadModule(fm *Frame, r diag.Ranger, spec string) (Ns, error) {
if strings.HasPrefix(spec, "./") || strings.HasPrefix(spec, "../") {
var dir string
if fm.srcMeta.IsFile {
dir = filepath.Dir(fm.srcMeta.Name)
} else {
var err error
dir, err = os.Getwd()
if err != nil {
return nil, err
}
}
path := filepath.Clean(dir + "/" + spec + ".elv")
return loadModuleFile(fm, r, spec, path)
}
if ns, ok := fm.Evaler.modules[spec]; ok {
return ns, nil
}
if code, ok := fm.bundled[spec]; ok {
return evalModule(fm, r, spec,
parse.Source{Name: "[bundled " + spec + "]", Code: code})
}
if fm.libDir == "" {
return nil, noSuchModule{spec}
}
return loadModuleFile(fm, r, spec, fm.libDir+"/"+spec+".elv")
}
func loadModuleFile(fm *Frame, r diag.Ranger, spec, path string) (Ns, error) {
if ns, ok := fm.modules[path]; ok {
return ns, nil
}
code, err := readFileUTF8(path)
if err != nil {
if os.IsNotExist(err) {
return nil, noSuchModule{spec}
}
return nil, err
}
return evalModule(fm, r, path, parse.Source{Name: path, Code: code, IsFile: true})
}
func evalModule(fm *Frame, r diag.Ranger, key string, src parse.Source) (Ns, error) {
tree, err := parse.Parse(src)
if err != nil {
return nil, err
}
// Make an empty scope to evaluate the module in.
modGlobal := Ns{}
newFm := &Frame{
fm.Evaler, src,
modGlobal, make(Ns),
fm.intCh, fm.ports,
fm.addTraceback(r), false,
}
op, err := compile(newFm.Builtin.static(), modGlobal.static(), tree, fm.ports[2].File)
if err != nil {
return nil, err
}
// Load the namespace before executing. This prevent circular "use"es from
// resulting in an infinite recursion.
fm.Evaler.modules[key] = modGlobal
err = newFm.Eval(op)
if err != nil {
// Unload the namespace.
delete(fm.modules, key)
return nil, err
}
return modGlobal, nil
}
// compileAnd compiles the "and" special form.
//
// The and special form evaluates arguments until a false-ish values is found
// and outputs it; the remaining arguments are not evaluated. If there are no
// false-ish values, the last value is output. If there are no arguments, it
// outputs $true, as if there is a hidden $true before actual arguments.
func compileAnd(cp *compiler, fn *parse.Form) effectOpBody {
return &andOrOp{cp.compoundOps(fn.Args), true, false}
}
// compileOr compiles the "or" special form.
//
// The or special form evaluates arguments until a true-ish values is found and
// outputs it; the remaining arguments are not evaluated. If there are no
// true-ish values, the last value is output. If there are no arguments, it
// outputs $false, as if there is a hidden $false before actual arguments.
func compileOr(cp *compiler, fn *parse.Form) effectOpBody {
return &andOrOp{cp.compoundOps(fn.Args), false, true}
}
type andOrOp struct {
argOps []valuesOp
init bool
stopAt bool
}
func (op *andOrOp) invoke(fm *Frame) error {
var lastValue interface{} = vals.Bool(op.init)
for _, argOp := range op.argOps {
values, err := argOp.exec(fm)
if err != nil {
return err
}
for _, value := range values {
if vals.Bool(value) == op.stopAt {
fm.OutputChan() <- value
return nil
}
lastValue = value
}
}
fm.OutputChan() <- lastValue
return nil
}
func compileIf(cp *compiler, fn *parse.Form) effectOpBody {
args := cp.walkArgs(fn)
var condNodes []*parse.Compound
var bodyNodes []*parse.Primary
for {
condNodes = append(condNodes, args.next())
bodyNodes = append(bodyNodes, args.nextMustLambda())
if !args.nextIs("elif") {
break
}
}
elseNode := args.nextMustLambdaIfAfter("else")
args.mustEnd()
condOps := cp.compoundOps(condNodes)
bodyOps := cp.primaryOps(bodyNodes)
var elseOp valuesOp
if elseNode != nil {
elseOp = cp.primaryOp(elseNode)
}
return &ifOp{condOps, bodyOps, elseOp}
}
type ifOp struct {
condOps []valuesOp
bodyOps []valuesOp
elseOp valuesOp
}
func (op *ifOp) invoke(fm *Frame) error {
bodies := make([]Callable, len(op.bodyOps))
for i, bodyOp := range op.bodyOps {
bodies[i] = bodyOp.execlambdaOp(fm)
}
elseFn := op.elseOp.execlambdaOp(fm)
for i, condOp := range op.condOps {
condValues, err := condOp.exec(fm.fork("if cond"))
if err != nil {
return err
}
if allTrue(condValues) {
return bodies[i].Call(fm.fork("if body"), NoArgs, NoOpts)
}
}
if op.elseOp.body != nil {
return elseFn.Call(fm.fork("if else"), NoArgs, NoOpts)
}
return nil
}
func compileWhile(cp *compiler, fn *parse.Form) effectOpBody {
args := cp.walkArgs(fn)
condNode := args.next()
bodyNode := args.nextMustLambda()
elseNode := args.nextMustLambdaIfAfter("else")
args.mustEnd()
condOp := cp.compoundOp(condNode)
bodyOp := cp.primaryOp(bodyNode)
var elseOp valuesOp
if elseNode != nil {
elseOp = cp.primaryOp(elseNode)
}
return &whileOp{condOp, bodyOp, elseOp}
}
type whileOp struct {
condOp, bodyOp, elseOp valuesOp
}
func (op *whileOp) invoke(fm *Frame) error {
body := op.bodyOp.execlambdaOp(fm)
elseBody := op.elseOp.execlambdaOp(fm)
iterated := false
for {
condValues, err := op.condOp.exec(fm.fork("while cond"))
if err != nil {
return err
}
if !allTrue(condValues) {
break
}
iterated = true
err = body.Call(fm.fork("while"), NoArgs, NoOpts)
if err != nil {
exc := err.(*Exception)
if exc.Reason == Continue {
// do nothing
} else if exc.Reason == Break {
break
} else {
return err
}
}
}
if op.elseOp.body != nil && !iterated {
return elseBody.Call(fm.fork("while else"), NoArgs, NoOpts)
}
return nil
}
func compileFor(cp *compiler, fn *parse.Form) effectOpBody {
args := cp.walkArgs(fn)
varNode := args.next()
iterNode := args.next()
bodyNode := args.nextMustLambda()
elseNode := args.nextMustLambdaIfAfter("else")
args.mustEnd()
varOp, restOp := cp.lvaluesOp(varNode.Indexings[0])
if restOp.body != nil {
cp.errorpf(restOp, "rest not allowed")
}
iterOp := cp.compoundOp(iterNode)
bodyOp := cp.primaryOp(bodyNode)
var elseOp valuesOp
if elseNode != nil {
elseOp = cp.primaryOp(elseNode)
}
return &forOp{varOp, iterOp, bodyOp, elseOp}
}
type forOp struct {
varOp lvaluesOp
iterOp valuesOp
bodyOp valuesOp
elseOp valuesOp
}
func (op *forOp) invoke(fm *Frame) error {
variable, err := evalForVar(fm, op.varOp, "iterator")
if err != nil {
return err
}
iterable, err := evalForValue(fm, op.iterOp, "value being iterated")
if err != nil {
return err
}
body := op.bodyOp.execlambdaOp(fm)
elseBody := op.elseOp.execlambdaOp(fm)
iterated := false
var errElement error
errIterate := vals.Iterate(iterable, func(v interface{}) bool {
iterated = true
err := variable.Set(v)
if err != nil {
errElement = err
return false
}
err = body.Call(fm.fork("for"), NoArgs, NoOpts)
if err != nil {
exc := err.(*Exception)
if exc.Reason == Continue {
// do nothing
} else if exc.Reason == Break {
return false
} else {
errElement = err
return false
}
}
return true
})
if errIterate != nil {
return errIterate
}
if errElement != nil {
return errElement
}
if !iterated && elseBody != nil {
return elseBody.Call(fm.fork("for else"), NoArgs, NoOpts)
}
return nil
}
func compileTry(cp *compiler, fn *parse.Form) effectOpBody {
logger.Println("compiling try")
args := cp.walkArgs(fn)
bodyNode := args.nextMustLambda()
logger.Printf("body is %q", parse.SourceText(bodyNode))
var exceptVarNode *parse.Indexing
var exceptNode *parse.Primary
if args.nextIs("except") {
logger.Println("except-ing")
n := args.peek()
// Is this a variable?
if len(n.Indexings) == 1 && n.Indexings[0].Head.Type == parse.Bareword {
exceptVarNode = n.Indexings[0]
args.next()
}
exceptNode = args.nextMustLambda()
}
elseNode := args.nextMustLambdaIfAfter("else")
finallyNode := args.nextMustLambdaIfAfter("finally")
args.mustEnd()
var exceptVarOp lvaluesOp
var bodyOp, exceptOp, elseOp, finallyOp valuesOp
bodyOp = cp.primaryOp(bodyNode)
if exceptVarNode != nil {
var restOp lvaluesOp
exceptVarOp, restOp = cp.lvaluesOp(exceptVarNode)
if restOp.body != nil {
cp.errorpf(restOp, "may not use @rest in except variable")
}
}
if exceptNode != nil {
exceptOp = cp.primaryOp(exceptNode)
}
if elseNode != nil {
elseOp = cp.primaryOp(elseNode)
}
if finallyNode != nil {
finallyOp = cp.primaryOp(finallyNode)
}
return &tryOp{bodyOp, exceptVarOp, exceptOp, elseOp, finallyOp}
}
type tryOp struct {
bodyOp valuesOp
exceptVarOp lvaluesOp
exceptOp valuesOp
elseOp valuesOp
finallyOp valuesOp
}
func (op *tryOp) invoke(fm *Frame) error {
body := op.bodyOp.execlambdaOp(fm)
exceptVar, err := op.exceptVarOp.execMustOne(fm)
if err != nil {
return err
}
except := op.exceptOp.execlambdaOp(fm)
elseFn := op.elseOp.execlambdaOp(fm)
finally := op.finallyOp.execlambdaOp(fm)
err = body.Call(fm.fork("try body"), NoArgs, NoOpts)
if err != nil {
if except != nil {
if exceptVar != nil {
err := exceptVar.Set(err.(*Exception))
if err != nil {
return err
}
}
err = except.Call(fm.fork("try except"), NoArgs, NoOpts)
}
} else {
if elseFn != nil {
err = elseFn.Call(fm.fork("try else"), NoArgs, NoOpts)
}
}
if finally != nil {
errFinally := finally.Call(fm.fork("try finally"), NoArgs, NoOpts)
if errFinally != nil {
// TODO: If err is not nil, this discards err. Use something similar
// to pipeline exception to expose both.
return errFinally
}
}
return err
}
// execLambdaOp executes a ValuesOp that is known to yield a lambda and returns
// the lambda. If the ValuesOp is empty, it returns a nil.
func (op valuesOp) execlambdaOp(fm *Frame) Callable {
if op.body == nil {
return nil
}
values, err := op.exec(fm)
if err != nil {
panic("must not be erroneous")
}
return values[0].(Callable)
}
// execMustOne executes the LValuesOp and returns an error if it does not
// evaluate to exactly one Variable. If the given LValuesOp is empty, it returns
// nil.
func (op lvaluesOp) execMustOne(fm *Frame) (vars.Var, error) {
if op.body == nil {
return nil, nil
}
variables, err := op.exec(fm)
if err != nil {
return nil, err
}
if len(variables) != 1 {
return nil, fm.errorpf(op, "should be one variable")
}
return variables[0], nil
}