-
Notifications
You must be signed in to change notification settings - Fork 2
/
infer.go
695 lines (664 loc) · 20.5 KB
/
infer.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
// The MIT License (MIT)
//
// Copyright (c) 2019 West Damron
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
package poly
import (
"errors"
"github.com/wdamron/poly/ast"
"github.com/wdamron/poly/internal/astutil"
"github.com/wdamron/poly/types"
)
func (ti *InferenceContext) infer(env *TypeEnv, level uint, e ast.Expr) (ret types.Type, err error) {
current := env.common.CurrentExpr
env.common.CurrentExpr = e
ret, err = ti.inferCurrentExpr(env, level)
env.common.CurrentExpr = current
return
}
func (ti *InferenceContext) inferCurrentExpr(env *TypeEnv, level uint) (ret types.Type, err error) {
switch e := env.common.CurrentExpr.(type) {
case *ast.Literal:
var using []types.Type
// Lookup types for variables bound within the literal:
if len(e.Using) != 0 {
using = make([]types.Type, len(e.Using))
for i, name := range e.Using {
vt := env.Lookup(name)
if vt == nil {
return nil, errors.New("Variable " + name + " is not defined")
}
using[i] = vt
}
}
// Construct and instantiate the literal with the bound variable types:
t, err := e.Construct(env, level, using)
if err != nil {
ti.invalid, ti.err = e, err
return t, err
}
t = env.common.Instantiate(level, t)
if ti.annotate {
e.SetType(t)
}
return t, nil
case *ast.Var:
var t types.Type
var scope *ast.Scope
if ti.annotate {
t, scope = env.scopeLookup(e.Name)
} else {
t = env.Lookup(e.Name)
}
if t == nil {
ti.invalid, ti.err = e, errors.New("Variable "+e.Name+" is not defined")
return nil, ti.err
}
t = env.common.Instantiate(level, t)
if ti.annotate {
e.SetType(t)
e.SetScope(scope)
}
return t, nil
case *ast.Deref:
t, err := ti.infer(env, level, e.Ref)
if err != nil {
return nil, err
}
tv := env.common.VarTracker.New(level)
tv.SetWeak()
if err := env.common.Unify(types.NewRef(tv), t); err != nil {
ti.invalid, ti.err = e, err
return t, err
}
t = types.RealType(tv)
if ti.annotate {
e.SetType(t)
}
return t, nil
case *ast.DerefAssign:
ref, err := ti.infer(env, level, e.Ref)
if err != nil {
return ref, err
}
tv := env.common.VarTracker.New(level)
tv.SetWeak()
if err := env.common.Unify(types.NewRef(tv), ref); err != nil {
ti.invalid, ti.err = e, err
return ref, err
}
val, err := ti.infer(env, level, e.Value)
if err != nil {
return ref, err
}
if err := env.common.Unify(tv, val); err != nil {
ti.invalid, ti.err = e, err
return ref, err
}
ref = types.RealType(ref)
if ti.annotate {
e.SetType(ref)
}
return ref, nil
case *ast.Pipe:
// Inline equivalent to inferring as nested (non-recursive) let-bindings:
t, err := ti.infer(env, level+1, e.Source)
if err != nil {
return nil, err
}
if len(e.Sequence) == 0 {
if ti.annotate {
e.SetType(t)
}
return t, nil
}
stashed := env.common.Stash(env, e.As)
env.common.EnterScope(e)
env.common.PushVarScope(e.As)
for _, step := range e.Sequence {
// Reassign the placeholder:
env.Assign(e.As, GeneralizeAtLevel(level, t))
t, err = ti.infer(env, level, step)
}
if ti.annotate && err != nil {
e.SetType(t)
}
// Restore the parent scope:
env.Remove(e.As)
env.common.Unstash(env, stashed)
env.common.LeaveScope()
return t, err
case *ast.ControlFlow:
// Loops are detected through SCC analysis and inferred as recursive functions.
// Blocks are inferred in dependency order:
env.common.EnterScope(e)
t, err := ti.inferControlFlow(env, level, e)
env.common.LeaveScope()
return t, err
case *ast.Let:
var t types.Type
env.common.EnterScope(e)
env.common.PushVarScope(e.Var)
stashed := 0
// Infer the binding type:
switch binding := e.Value.(type) {
case *ast.Func:
// Allow self-references within function types:
varType := env.common.VarTracker.New(level + 1)
// Begin a new scope:
stashed = env.common.Stash(env, e.Var)
env.Assign(e.Var, varType)
t, err := ti.infer(env, level+1, binding)
if err != nil {
goto RestoreScope
}
if err := env.common.Unify(varType, t); err != nil {
ti.invalid, ti.err = e, err
goto RestoreScope
}
GeneralizeAtLevel(level, varType)
default:
t, err := ti.infer(env, level+1, binding)
if err != nil {
env.common.LeaveScope()
return nil, err
}
// Begin a new scope:
stashed = env.common.Stash(env, e.Var)
env.Assign(e.Var, GeneralizeAtLevel(level, t))
}
// Infer the body type:
t, _ = ti.infer(env, level, e.Body)
RestoreScope:
// Restore the parent scope:
env.Remove(e.Var)
env.common.Unstash(env, stashed)
env.common.PopVarScope(e.Var)
env.common.LeaveScope()
return t, ti.err
case *ast.LetGroup:
// Grouped let-bindings are sorted into strongly-connected components, then type-checked in dependency order:
env.common.EnterScope(e)
t, err := ti.inferLetGroup(env, level, e)
env.common.LeaveScope()
return t, err
case *ast.Func:
args := make([]types.Type, len(e.ArgNames))
stashed := 0
vars := env.common.VarTracker.NewList(level, len(e.ArgNames))
tv, tail := vars.Head(), vars.Tail()
// Begin a new scope:
env.common.EnterScope(e)
for i, name := range e.ArgNames {
stashed += env.common.Stash(env, name)
args[i] = tv
env.Assign(name, tv)
env.common.PushVarScope(name)
tv, tail = tail.Head(), tail.Tail()
}
ret, err := ti.infer(env, level, e.Body)
for _, name := range e.ArgNames {
env.Remove(name)
env.common.PopVarScope(name)
}
// Restore the parent scope:
env.common.LeaveScope()
env.common.Unstash(env, stashed)
t := &types.Arrow{Args: args, Return: ret}
if ti.annotate {
e.SetType(t)
}
return t, err
case *ast.Call:
ft, err := ti.infer(env, level, e.Func)
if err != nil {
return nil, err
}
// If t is an unbound type-variable, instantiate a function with unbound type-variables for its
// arguments and return value; otherwise, ensure t has the correct argument count.
arrow, err := ti.matchFuncType(env, len(e.Args), ft)
if err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
args, ret := arrow.Args, arrow.Return
for i, arg := range e.Args {
ta, err := ti.infer(env, level, arg)
if err != nil {
return nil, err
}
if err := env.common.Unify(args[i], ta); err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
}
if ti.annotate {
arrow, _ := ft.(*types.Arrow)
e.SetFuncType(arrow)
e.SetType(ret)
}
return ret, nil
case *ast.RecordEmpty:
rt := &types.Record{Row: types.RowEmptyPointer}
if ti.annotate {
e.SetType(rt)
}
return rt, nil
case *ast.RecordSelect:
// label, rest := fresh(), fresh()
// unify({ <label>: label | rest }, record)
// -> label
label, _, err := ti.splitRecord(env, level, e.Record, e.Label)
if err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
return label, nil
case *ast.RecordRestrict:
// label, rest := fresh(), fresh()
// unify({ <label>: label | rest }, record)
// -> rest
_, rest, err := ti.splitRecord(env, level, e.Record, e.Label)
if err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
return rest, nil
case *ast.RecordExtend:
mb := types.NewTypeMapBuilder()
for _, label := range e.Labels {
t, err := ti.infer(env, level, label.Value)
if err != nil {
return nil, err
}
mb.Set(label.Label, types.SingletonTypeList(t))
}
rowType := env.common.VarTracker.New(level)
recordType, err := ti.infer(env, level, e.Record)
if err != nil {
return nil, err
}
if err := env.common.Unify(&types.Record{Row: rowType}, recordType); err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
ext := &types.RowExtend{Row: rowType, Labels: mb.Build()}
labels, rest, err := types.FlattenRowType(ext)
if err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
ext.Labels, ext.Row = labels, rest
rt := &types.Record{Row: ext}
if ti.annotate {
e.SetType(rt)
}
return rt, nil
case *ast.Variant:
rowType := env.common.VarTracker.New(level)
variantType := env.common.VarTracker.New(level)
t, err := ti.infer(env, level, e.Value)
if err != nil {
return nil, err
}
if err := env.common.Unify(variantType, t); err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
labels := types.SingletonTypeMap(e.Label, variantType)
vt := &types.Variant{Row: &types.RowExtend{Row: rowType, Labels: labels}}
return vt, nil
case *ast.Match:
// Inline equivalent to inferring a record-select on a record constructed from the cases,
// where each case is represented as a labeled function from the case's variant-type to the
// shared return type for the match expression:
//
// variant := [:a 'a]
// handler := ({a : 'a -> 'result, b : 'b -> 'result})[variant.label]
// result := handler(variant.value)
var (
retType, rowType types.Type
err error
)
if e.Default == nil {
retType, rowType = env.common.VarTracker.New(level), types.RowEmptyPointer
} else {
rowType = env.common.VarTracker.New(level)
// Begin a new scope:
stashed := env.common.Stash(env, e.Default.Var)
env.common.EnterScope(e)
env.Assign(e.Default.Var, &types.Variant{Row: rowType})
env.common.PushVarScope(e.Default.Var)
retType, err = ti.infer(env, level, e.Default.Value)
// Restore the parent scope:
env.Remove(e.Default.Var)
env.common.Unstash(env, stashed)
env.common.PopVarScope(e.Default.Var)
env.common.LeaveScope()
if err != nil {
return nil, err
}
}
matchType, err := ti.infer(env, level, e.Value)
if err != nil {
return nil, err
}
env.common.EnterScope(e)
casesRow, err := ti.inferCases(env, level, retType, rowType, e, e.Cases)
env.common.LeaveScope()
if err != nil {
return nil, err
}
if err := env.common.Unify(matchType, &types.Variant{Row: casesRow}); err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
if ti.annotate {
e.SetType(retType)
}
return retType, nil
}
e := env.common.CurrentExpr
var exprName string
if e != nil {
exprName = "(" + e.ExprName() + ")"
} else {
exprName = "(nil)"
}
ti.invalid, ti.err = e, errors.New("Unhandled expression type "+exprName)
return nil, ti.err
}
// label, rest := fresh(), fresh()
// unify({ <label>: label | rest }, record)
// -> (label, rest)
func (ti *InferenceContext) splitRecord(env *TypeEnv, level uint, recordExpr ast.Expr, label string) (labelType types.Type, restType types.Type, err error) {
rowType := env.common.VarTracker.New(level)
labelType = env.common.VarTracker.New(level)
labels := types.SingletonTypeMap(label, labelType)
paramType := &types.Record{Row: &types.RowExtend{Row: rowType, Labels: labels}}
var recordType types.Type
recordType, err = ti.infer(env, level, recordExpr)
if err != nil {
return nil, nil, err
}
if err = env.common.Unify(paramType, recordType); err != nil {
return nil, nil, err
}
restType = &types.Record{Row: rowType}
return
}
// If t is an unbound type-variable, instantiate a function with unbound type-variables for its arguments and return value;
// otherwise, ensure t has the correct argument count.
func (ti *InferenceContext) matchFuncType(env *TypeEnv, argc int, t types.Type) (*types.Arrow, error) {
switch t := t.(type) {
case *types.Arrow:
if len(t.Args) != argc {
return t, errors.New("Unexpected number of arguments for applied function")
}
return t, nil
case *types.Var:
switch {
case t.IsLinkVar():
return ti.matchFuncType(env, argc, t.Link())
case t.IsUnboundVar():
args := make([]types.Type, argc)
vars := env.common.VarTracker.NewList(t.Level(), argc+1)
tv, tail := vars.Head(), vars.Tail()
for i := 0; i < argc; i++ {
args[i] = tv
tv, tail = tail.Head(), tail.Tail()
}
arrow := &types.Arrow{Args: args, Return: tv}
t.SetLink(arrow)
return arrow, nil
default:
return nil, errors.New("Type variable for applied function has not been instantiated")
}
}
return nil, errors.New("Unexpected type " + t.TypeName() + " for applied function")
}
// https://github.com/tomprimozic/type-systems/blob/master/extensible_rows2/infer.ml#L287
//
// infer_cases env level return_ty rest_row_ty cases = match cases with
// | [] -> rest_row_ty
// | (label, var_name, expr) :: other_cases ->
// let variant_ty = new_var level in
// unify return_ty (infer (Env.extend env var_name variant_ty) level expr) ;
// let other_cases_row = infer_cases env level return_ty rest_row_ty other_cases in
// TRowExtend(LabelMap.singleton label [variant_ty], other_cases_row)
func (ti *InferenceContext) inferCases(env *TypeEnv, level uint, retType, rowType types.Type, e *ast.Match, cases []ast.MatchCase) (types.Type, error) {
// Each case extends an existing record formed from all subsequent cases.
// Visit cases in reverse order, accumulating labels and value types into the record as row-extensions.
extensions := make([]types.RowExtend, len(cases))
vars := env.common.VarTracker.NewList(level, len(cases))
tv, tail := vars.Head(), vars.Tail()
for i := len(cases) - 1; i >= 0; i-- {
c := cases[i]
// Infer the return expression for the case with the variable-name temporarily bound in the environment:
variantType := tv
// Begin a new scope:
stashed := env.common.Stash(env, c.Var)
env.Assign(c.Var, variantType)
env.common.PushVarScope(c.Var)
c.SetVariantType(variantType)
t, err := ti.infer(env, level, c.Value)
env.Remove(c.Var)
env.common.PopVarScope(c.Var)
// Restore the parent scope:
env.common.Unstash(env, stashed)
if err != nil {
return nil, err
}
// Ensure all cases have matching return types:
if err := env.common.Unify(retType, t); err != nil {
return nil, err
}
// Extend the accumulated record:
extensions[i].Row, extensions[i].Labels = rowType, types.SingletonTypeMap(c.Label, variantType)
rowType = &extensions[i]
tv, tail = tail.Head(), tail.Tail()
}
// Return the accumulated record which maps each variant label to its associated type(s):
return rowType, nil
}
// Grouped let-bindings are sorted into strongly-connected components, then type-checked in dependency order.
func (ti *InferenceContext) inferLetGroup(env *TypeEnv, level uint, e *ast.LetGroup) (ret types.Type, err error) {
if !ti.analyzed {
if ti.analysis == nil {
ti.analysis = new(astutil.Analysis)
ti.analysis.Init()
}
if err := ti.analysis.Analyze(ti.rootExpr); err != nil {
ti.invalid, ti.err, ti.analysis.Invalid = ti.analysis.Invalid, err, nil
return nil, err
}
ti.analyzed = true
}
for _, v := range e.Vars {
env.common.PushVarScope(v.Var)
}
stashed, sccs := 0, ti.analysis.SCC[ti.letGroupCount]
ti.letGroupCount++
// Grouped let-bindings are sorted into strongly-connected components, then type-checked in dependency order:
for _, scc := range sccs {
// Add fresh type-variables for bindings:
vars := env.common.VarTracker.NewList(level+1, len(scc))
tv, tail := vars.Head(), vars.Tail()
// Begin a new scope:
for _, bindNum := range scc {
v := e.Vars[bindNum]
stashed += env.common.Stash(env, v.Var)
env.Assign(v.Var, tv)
tv, tail = tail.Head(), tail.Tail()
}
// Infer types:
tv, tail = vars.Head(), vars.Tail()
for _, bindNum := range scc {
v := e.Vars[bindNum]
var isFunc bool
// To prevent self-references within non-function types, stash/remove the type-variable:
if _, isFunc = v.Value.(*ast.Func); !isFunc {
exists := false
for i := 0; i < stashed; i++ {
existing := env.common.EnvStash[len(env.common.EnvStash)-(1+i)]
if existing.Name == v.Var {
env.Assign(v.Var, existing.Type)
exists = true
break
}
}
if !exists {
env.Remove(v.Var)
}
}
t, err := ti.infer(env, level+1, v.Value)
if err != nil {
return nil, err
}
if err := env.common.Unify(tv, t); err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
// Restore the previously stashed/removed type-variable:
if !isFunc {
env.Assign(v.Var, tv)
}
tv, tail = tail.Head(), tail.Tail()
}
// Generalize types:
tv, tail = vars.Head(), vars.Tail()
for _, bindNum := range scc {
v := e.Vars[bindNum]
env.Assign(v.Var, GeneralizeAtLevel(level, tv))
tv, tail = tail.Head(), tail.Tail()
}
}
t, err := ti.infer(env, level, e.Body)
// Restore the parent scope:
for _, v := range e.Vars {
env.Remove(v.Var)
env.common.PopVarScope(v.Var)
}
env.common.Unstash(env, stashed)
if err == nil && ti.annotate {
sccBindings := make([][]ast.LetBinding, len(sccs))
for i, scc := range sccs {
cycle := make([]ast.LetBinding, len(scc))
for j, binding := range scc {
cycle[j] = e.Vars[binding]
}
sccBindings[i] = cycle
}
e.SetStronglyConnectedComponents(sccBindings)
}
return t, err
}
// Loops are detected through SCC analysis and inferred as recursive functions. Blocks are inferred in dependency order.
func (ti *InferenceContext) inferControlFlow(env *TypeEnv, level uint, e *ast.ControlFlow) (ret types.Type, err error) {
// Evaluate all sub-expressions in a new scope with local variables bound to mutable references:
stashed := 0
refs := make([]*types.App, len(e.Locals))
vars := env.common.VarTracker.NewList(level, len(e.Locals))
tv, tail := vars.Head(), vars.Tail()
for i, name := range e.Locals {
stashed += env.common.Stash(env, name)
tv.SetWeak()
ref := types.NewRef(tv)
env.Assign(name, ref)
env.common.PushVarScope(name)
refs[i] = ref
tv, tail = tail.Head(), tail.Tail()
}
// Loops are detected through SCC analysis and inferred as recursive functions. Ensure all blocks and
// cycles in the strongly connected components for e reach the return block, directly or transitively:
sccs, err := e.Validate(ti.annotate)
if err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
var tmpRefs []*types.App
// Blocks will be inferred in dependency order:
for _, cycle := range sccs {
// A component with a single block which doesn't jump to itself is not a cycle or part of a cycle:
if len(cycle) == 1 && !e.HasJump(cycle[0], cycle[0]) {
block := cycle[0]
for i, sub := range block.Sequence {
t, err := ti.infer(env, level, sub)
if err != nil {
return nil, err
}
// The last expression within the return block determines the return type:
if block.IsReturn() && i == len(block.Sequence)-1 {
ret = t
if ti.annotate {
e.SetType(t)
}
}
}
continue
}
// A component with more than 1 block or a single block which jumps to itself is a cycle.
// Cycles (loops) are inferred similarly to recursive functions.
//
// Evaluate all sub-expressions in a new scope with local variables bound to mutable references:
if len(tmpRefs) == 0 {
tmpRefs = make([]*types.App, len(e.Locals))
}
vars := env.common.VarTracker.NewList(level, len(e.Locals))
tv, tail := vars.Head(), vars.Tail()
for i, name := range e.Locals {
tv.SetWeak()
ref := types.NewRef(tv)
env.Assign(name, ref)
tmpRefs[i] = ref
tv, tail = tail.Head(), tail.Tail()
}
for _, block := range cycle {
// The entry and return blocks are handled above (as non-cycles).
for _, sub := range block.Sequence {
if _, err := ti.infer(env, level, sub); err != nil {
return nil, err
}
}
}
// Check consistent usage of locals across loop iterations:
for i, ref := range refs {
if err := env.common.Unify(ref, tmpRefs[i]); err != nil {
ti.invalid, ti.err = e, err
return nil, err
}
}
// Restore the previous scope:
for i, name := range e.Locals {
env.Assign(name, refs[i])
}
}
// Restore the parent scope:
for _, name := range e.Locals {
env.Remove(name)
env.common.PopVarScope(name)
}
env.common.Unstash(env, stashed)
if ret == nil {
ti.invalid, ti.err = e, errors.New("Control flow must reach the return block and return a value")
return nil, ti.err
}
return ret, nil
}