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parse.go
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parse.go
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// Copyright (c) 2014, Rob Thornton
// All rights reserved.
// This source code is governed by a Simplied BSD-License. Please see the
// LICENSE included in this distribution for a copy of the full license
// or, if one is not included, you may also find a copy at
// http://opensource.org/licenses/BSD-2-Clause
// Package parse implements the parser for the Calc programming language
package parse
import (
"fmt"
"io/ioutil"
"os"
"path/filepath"
"reflect"
"github.com/rthornton128/calc/ast"
"github.com/rthornton128/calc/scan"
"github.com/rthornton128/calc/token"
)
// ParseExpression parses the given source string and returns an ast.Node
// representing the root of the expression. This function is intended to
// facilitate testing and is not use by the compiler itself. The name is
// used in error reporting
func ParseExpression(name, src string) (ast.Node, error) {
var p parser
fset := token.NewFileSet()
file := fset.Add(name, src)
p.init(file, name, string(src), nil)
node := p.parseGenExpr()
if p.errors.Count() > 0 {
return nil, p.errors
}
return node, nil
}
// ParseFile parses the file identified by filename and returns a pointer
// to an ast.File object. The file should contain Calc source code and
// have the .calc file extension.
// The returned AST object ast.File is nil if there is an error.
func ParseFile(fset *token.FileSet, filename string, s *ast.Scope) (*ast.File, error) {
fi, err := os.Stat(filename)
if err != nil {
return nil, err
}
var p parser
var f *ast.File
if ext := filepath.Ext(fi.Name()); ext != ".calc" {
return nil, fmt.Errorf("unknown file extension, must be .calc")
}
src, err := ioutil.ReadFile(filename)
if err != nil {
return nil, err
}
file := fset.Add(filepath.Base(filename), string(src))
p.init(file, filename, string(src), s)
f = p.parseFile()
if p.errors.Count() > 0 {
return nil, p.errors
}
return f, nil
}
// ParseDir parses a directory of Calc source files. It calls ParseFile
// for each file ending in .calc found in the directory.
func ParseDir(fset *token.FileSet, path string) (*ast.Package, error) {
fd, err := os.Open(path)
if err != nil {
return nil, err
}
defer fd.Close()
fnames, err := fd.Readdirnames(0)
if err != nil {
return nil, err
}
fnames = filterByExt(fnames)
if len(fnames) == 0 {
return nil, fmt.Errorf("no files to parse; stop")
}
var files []*ast.File
scope := ast.NewScope(nil)
// TODO: use concurrency
for _, name := range fnames {
f, err := ParseFile(fset, filepath.Join(path, name), scope)
if f == nil {
return nil, err
}
files = append(files, f)
}
return &ast.Package{Scope: scope, Files: files}, nil
}
func filterByExt(names []string) []string {
filtered := make([]string, 0, len(names))
for _, name := range names {
if filepath.Ext(name) == ".calc" {
filtered = append(filtered, name)
}
}
return filtered
}
type parser struct {
file *token.File
errors token.ErrorList
scanner scan.Scanner
listok bool
curScope *ast.Scope
topScope *ast.Scope
pos token.Pos
tok token.Token
lit string
}
/* Utility */
func (p *parser) addError(args ...interface{}) {
p.errors.Add(p.file.Position(p.pos), args...)
}
func (p *parser) checkExpr(e ast.Expr) ast.Expr {
if e != nil && !reflect.ValueOf(e).IsNil() {
switch t := e.(type) {
case *ast.BasicLit, *ast.BinaryExpr, *ast.CallExpr, *ast.Ident, *ast.IfExpr,
*ast.UnaryExpr:
case *ast.ExprList:
p.checkExpr(t.List[len(t.List)-1])
default:
// TODO: should be part of addError
p.errors.Add(p.file.Position(e.Pos()), "expression has no side-effects")
}
}
return e
}
func (p *parser) expect(tok token.Token) token.Pos {
pos := p.pos
if p.tok != tok {
p.addError("Expected '" + tok.String() + "' got '" + p.lit + "'")
}
p.next()
return pos
}
func (p *parser) init(file *token.File, fname, src string, s *ast.Scope) {
if s == nil {
s = ast.NewScope(nil)
}
p.file = file
p.scanner.Init(p.file, src)
p.listok = false
p.curScope = s //ast.NewScope(nil)
p.topScope = p.curScope
p.next()
}
func (p *parser) next() {
p.lit, p.tok, p.pos = p.scanner.Scan()
}
/* Scope */
func (p *parser) openScope() {
p.curScope = ast.NewScope(p.curScope)
}
func (p *parser) closeScope() {
p.curScope = p.curScope.Parent
}
/* Parsing */
func (p *parser) parseAssignExpr(open token.Pos) *ast.AssignExpr {
pos := p.expect(token.ASSIGN)
nam := p.parseIdent()
val := p.parseGenExpr()
end := p.expect(token.RPAREN)
return &ast.AssignExpr{
Expression: ast.Expression{Opening: open, Closing: end},
Equal: pos,
Name: nam,
Value: p.checkExpr(val),
}
}
func (p *parser) parseBasicLit() *ast.BasicLit {
pos, tok, lit := p.pos, p.tok, p.lit
p.next()
return &ast.BasicLit{LitPos: pos, Kind: tok, Lit: lit}
}
func (p *parser) parseBinaryExpr(open token.Pos) *ast.BinaryExpr {
pos := p.pos
op := p.tok
p.next()
var list []ast.Expr
for p.tok != token.RPAREN && p.tok != token.EOF {
list = append(list, p.parseGenExpr())
}
if len(list) < 2 {
p.addError("binary expression must have at least two operands")
}
end := p.expect(token.RPAREN)
return &ast.BinaryExpr{
Expression: ast.Expression{
Opening: open,
Closing: end,
},
Op: op,
OpPos: pos,
List: list,
}
}
func (p *parser) parseCallExpr(open token.Pos) *ast.CallExpr {
nam := p.parseIdent()
var list []ast.Expr
for p.tok != token.RPAREN && p.tok != token.EOF {
list = append(list, p.parseGenExpr())
}
end := p.expect(token.RPAREN)
return &ast.CallExpr{
Expression: ast.Expression{
Opening: open,
Closing: end,
},
Name: nam,
Args: list,
}
}
func (p *parser) parseDeclExpr(open token.Pos) *ast.DeclExpr {
if p.curScope != p.topScope {
p.addError("function declarations may only be used in top-level scope")
return nil
}
pos := p.expect(token.DECL)
nam := p.parseIdent()
p.openScope()
var list []*ast.Ident
if p.tok == token.LPAREN {
p.next()
list = p.parseParamList()
}
typ := p.parseIdent()
body := p.tryExprOrList()
end := p.expect(token.RPAREN)
decl := &ast.DeclExpr{
Expression: ast.Expression{
Opening: open,
Closing: end,
},
Decl: pos,
Name: nam,
Type: typ,
Params: list,
Body: p.checkExpr(body),
Scope: p.curScope,
}
ob := &ast.Object{
NamePos: nam.NamePos,
Name: nam.Name,
Kind: ast.Decl,
Type: typ,
Value: decl,
}
p.closeScope()
if old := p.curScope.Insert(ob); old != nil {
p.addError("redeclaration of function not allowed, originally declared "+
"at: ", p.file.Position(old.NamePos))
}
return decl
}
func (p *parser) parseExpr() ast.Expr {
var expr ast.Expr
listok := p.listok
pos := p.expect(token.LPAREN)
if p.listok && p.tok == token.LPAREN {
expr = p.parseExprList(pos)
return expr
}
p.listok = false
switch p.tok {
case token.ADD, token.SUB, token.MUL, token.QUO, token.REM,
token.EQL, token.GTE, token.GTT, token.NEQ, token.LST, token.LTE:
expr = p.parseBinaryExpr(pos)
case token.ASSIGN:
expr = p.parseAssignExpr(pos)
case token.DECL:
expr = p.parseDeclExpr(pos)
case token.IDENT:
expr = p.parseCallExpr(pos)
case token.IF:
expr = p.parseIfExpr(pos)
case token.VAR:
expr = p.parseVarExpr(pos)
default:
if listok {
p.addError("Expected expression but got '" + p.lit + "'")
} else {
p.addError("Expected operator, keyword or identifier but got '" + p.lit +
"'")
}
}
return expr
}
func (p *parser) parseExprList(open token.Pos) ast.Expr {
p.listok = false
var list []ast.Expr
for p.tok != token.RPAREN {
list = append(list, p.parseGenExpr())
}
if len(list) < 1 {
p.addError("empty expression list not allowed")
}
end := p.expect(token.RPAREN)
return &ast.ExprList{
Expression: ast.Expression{
Opening: open,
Closing: end,
},
List: list,
}
}
func (p *parser) parseGenExpr() ast.Expr {
var expr ast.Expr
switch p.tok {
case token.LPAREN:
expr = p.parseExpr()
case token.IDENT:
expr = p.parseIdent()
case token.INTEGER:
expr = p.parseBasicLit()
case token.SUB:
expr = p.parseUnaryExpr()
default:
p.addError("Expected expression, got '" + p.lit + "'")
p.next()
}
p.listok = false
return expr
}
func (p *parser) parseFile() *ast.File {
for p.tok != token.EOF {
p.parseGenExpr()
}
if p.topScope.Size() < 1 {
p.addError("reached end of file without any declarations")
}
return &ast.File{Scope: p.topScope}
}
func (p *parser) parseIdent() *ast.Ident {
name := p.lit
pos := p.expect(token.IDENT)
return &ast.Ident{NamePos: pos, Name: name}
}
func (p *parser) parseIfExpr(open token.Pos) *ast.IfExpr {
pos := p.expect(token.IF)
cond := p.parseGenExpr()
var typ *ast.Ident
if p.tok == token.IDENT {
typ = p.parseIdent()
}
p.openScope()
scope := p.curScope
then := p.tryExprOrList()
var els ast.Expr
if p.tok != token.RPAREN {
els = p.tryExprOrList()
}
p.closeScope()
end := p.expect(token.RPAREN)
return &ast.IfExpr{
Expression: ast.Expression{
Opening: open,
Closing: end,
},
If: pos,
Type: typ,
Cond: cond,
Then: then,
Else: els,
Scope: scope,
}
}
func (p *parser) parseParamList() []*ast.Ident {
var list []*ast.Ident
count, start := 0, 0
for p.tok != token.RPAREN {
ident := p.parseIdent()
count++
if p.tok == token.COMMA || p.tok == token.RPAREN {
for _, param := range list[start:] {
if param.Object == nil {
param.Object = &ast.Object{
Kind: ast.Var,
Name: param.Name,
}
}
param.Object.Type = ident
p.curScope.Insert(param.Object)
}
start = count
continue
}
list = append(list, ident)
}
if len(list) < 1 {
p.addError("empty param list not allowed")
}
p.expect(token.RPAREN)
return list
}
func (p *parser) parseUnaryExpr() *ast.UnaryExpr {
pos, op := p.pos, p.lit
p.next()
exp := p.parseGenExpr()
return &ast.UnaryExpr{OpPos: pos, Op: op, Value: p.checkExpr(exp)}
}
func (p *parser) parseVarExpr(open token.Pos) *ast.VarExpr {
var (
name *ast.Ident
vtype *ast.Ident
value *ast.AssignExpr
)
varpos := p.expect(token.VAR)
switch p.tok {
case token.IDENT:
name = p.parseIdent()
case token.LPAREN:
value = p.parseAssignExpr(p.expect(token.LPAREN))
name = value.Name
default:
name = &ast.Ident{token.NoPos, "NoName", nil}
p.addError("expected identifier or assignment")
}
if value == nil || p.tok == token.IDENT {
vtype = p.parseIdent()
}
end := p.expect(token.RPAREN)
ob := &ast.Object{
NamePos: name.NamePos,
Name: name.Name,
Kind: ast.Var,
Type: vtype,
Value: value,
}
if old := p.curScope.Insert(ob); old != nil {
p.addError("redeclaration of variable not allowed; original "+
"declaration at: ", p.file.Position(old.NamePos))
}
return &ast.VarExpr{
Expression: ast.Expression{Opening: open, Closing: end},
Var: varpos,
Name: name,
Object: ob,
}
}
func (p *parser) tryExprOrList() ast.Expr {
p.listok = true
return p.parseGenExpr()
}