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parser.go
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parser.go
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// Copyright 2021 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package slang
import (
"fmt"
"go/scanner"
"go/token"
"reflect"
"runtime"
"strings"
)
type statement struct {
pos token.Position
results, args []tokPos
assign bool
verbName tokPos
}
type statements []statement
func parseBytes(src []byte) (statements, error) {
tokens, err := scanBytes(src)
if err != nil {
return nil, err
}
return parse(tokens)
}
func parseFile(filename string) (statements, error) {
tokens, err := scanFile(filename)
if err != nil {
return nil, err
}
return parse(tokens)
}
func writeCommaSep(out *strings.Builder, idents []tokPos) {
for i, tp := range idents {
out.WriteString(tp.lit)
if tp.ellipsis {
out.WriteString("...")
}
if i < len(idents)-1 {
out.WriteString(", ")
}
}
}
func (s statement) String() string {
out := &strings.Builder{}
formatStatement(out, s)
return out.String()
}
func formatStatement(out *strings.Builder, s statement) {
if len(s.results) > 0 {
writeCommaSep(out, s.results)
if s.assign {
out.WriteString(" = ")
} else {
out.WriteString(" := ")
}
}
out.WriteString(s.verbName.lit)
out.WriteRune('(')
writeCommaSep(out, s.args)
out.WriteRune(')')
}
func (stmts statements) String() string {
out := &strings.Builder{}
for _, s := range stmts {
formatStatement(out, s)
out.WriteRune('\n')
}
return out.String()
}
type parseState struct {
scratch []tokPos
assign bool
results []tokPos
verbName tokPos
args []tokPos
statements statements
errs scanner.ErrorList
}
type parseStateFn func(tokPos) parseStateFn
func (ps *parseState) resultsIdent(tp tokPos) parseStateFn {
if tp.tok == token.IDENT {
ps.scratch = append(ps.scratch, tp)
return ps.resultsCommaOrDefineOrArgs
}
ps.errs = append(ps.errs, &scanner.Error{
Pos: tp.pos,
Msg: fmt.Sprintf("expected variable name, got '%s'", tp.tok),
})
return ps.resultsIdent
}
func (ps *parseState) resultsCommaOrDefineOrArgs(tp tokPos) parseStateFn {
switch tp.tok {
case token.COMMA:
return ps.resultsIdent
case token.DEFINE, token.ASSIGN:
ps.results = make([]tokPos, len(ps.scratch))
copy(ps.results, ps.scratch)
ps.scratch = ps.scratch[:0]
ps.assign = tp.tok == token.ASSIGN
return ps.funcName
case token.LPAREN:
// function call with no results.
if len(ps.scratch) == 1 {
ps.verbName = ps.scratch[0]
ps.scratch = ps.scratch[:0]
return ps.argIdentOrRightParen
}
}
ps.errs = append(ps.errs, &scanner.Error{
Pos: tp.pos,
Msg: fmt.Sprintf("expected ',' or ':=', got '%s'", tp.tok),
})
return ps.resultsCommaOrDefineOrArgs
}
func (ps *parseState) funcName(tp tokPos) parseStateFn {
if tp.tok == token.IDENT {
ps.verbName = tp
return ps.argsLeftParen
}
ps.errs = append(ps.errs, &scanner.Error{
Pos: tp.pos,
Msg: fmt.Sprintf("expected function name, got '%s'", tp.tok),
})
return ps.resultsIdent
}
func (ps *parseState) argsLeftParen(tp tokPos) parseStateFn {
if tp.tok == token.LPAREN {
return ps.argIdentOrRightParen
}
ps.errs = append(ps.errs, &scanner.Error{
Pos: tp.pos,
Msg: fmt.Sprintf("expected '(', got '%s'", tp.tok),
})
return ps.argsLeftParen
}
func (ps *parseState) argIdentOrRightParen(tp tokPos) parseStateFn {
if tp.tok == token.RPAREN {
return ps.done
}
return ps.argIdent(tp)
}
func (ps *parseState) argIdent(tp tokPos) parseStateFn {
switch tp.tok {
case token.IDENT, token.STRING, token.INT:
ps.scratch = append(ps.scratch, tp)
return ps.argsCommaOrEllipsisOrRightParen
}
ps.errs = append(ps.errs, &scanner.Error{
Pos: tp.pos,
Msg: fmt.Sprintf("expected variable or literal, got '%s'", tp.tok),
})
return ps.resultsIdent
}
func (ps *parseState) argRightParen(tp tokPos) parseStateFn {
if tp.tok == token.RPAREN {
ps.args = make([]tokPos, len(ps.scratch))
copy(ps.args, ps.scratch)
ps.scratch = ps.scratch[:0]
return ps.done
}
ps.errs = append(ps.errs, &scanner.Error{
Pos: tp.pos,
Msg: fmt.Sprintf("expected ')' got '%s'", tp.tok),
})
return ps.done
}
func (ps *parseState) argsCommaOrEllipsisOrRightParen(tp tokPos) parseStateFn {
switch tp.tok {
case token.COMMA:
return ps.argIdent
case token.RPAREN:
return ps.argRightParen(tp)
case token.ELLIPSIS:
if len(ps.scratch) == 0 {
ps.errs = append(ps.errs, &scanner.Error{
Pos: tp.pos,
Msg: "unexpected '...'",
})
return ps.done
}
ps.scratch[len(ps.scratch)-1].ellipsis = true
return ps.argRightParen
}
ps.errs = append(ps.errs, &scanner.Error{
Pos: tp.pos,
Msg: fmt.Sprintf("expected ',' or ')', got '%s'", tp.tok),
})
return ps.argsCommaOrEllipsisOrRightParen
}
func (ps *parseState) copyStatementAndReset() statement {
stmt := statement{
results: ps.results,
args: ps.args,
verbName: ps.verbName,
assign: ps.assign,
}
if len(ps.results) > 0 {
stmt.pos = ps.results[0].pos
} else {
stmt.pos = ps.verbName.pos
}
ps.results, ps.args = nil, nil
ps.assign = false
ps.verbName = tokPos{}
return stmt
}
func (ps *parseState) done(tp tokPos) parseStateFn {
if tp.tok == token.SEMICOLON {
stmt := ps.copyStatementAndReset()
ps.statements = append(ps.statements, stmt)
return ps.resultsIdent
}
ps.errs = append(ps.errs, &scanner.Error{
Pos: tp.pos,
Msg: fmt.Sprintf("expected '; or '\\n', got '%s'", tp.tok),
})
return ps.done
}
var parseTrace = false
func parse(tokens []tokPos) (statements, error) {
ps := &parseState{}
fn := ps.resultsIdent
for _, tp := range tokens {
if parseTrace {
fmt.Printf("parse: %v: %v: %v\n", tp.pos, tp.tok, runtime.FuncForPC(reflect.ValueOf(fn).Pointer()).Name())
}
fn = fn(tp)
if len(ps.errs) > 5 {
return nil, ps.errs.Err()
}
}
return ps.statements, ps.errs.Err()
}