package main
import (
"bufio"
"fmt"
"log"
"os"
"strconv"
"strings"
)
type TokenType int
const (
tkEOI TokenType = iota
tkMul
tkDiv
tkMod
tkAdd
tkSub
tkNegate
tkNot
tkLss
tkLeq
tkGtr
tkGeq
tkEql
tkNeq
tkAssign
tkAnd
tkOr
tkIf
tkElse
tkWhile
tkPrint
tkPutc
tkLparen
tkRparen
tkLbrace
tkRbrace
tkSemi
tkComma
tkIdent
tkInteger
tkString
)
type NodeType int
const (
ndIdent NodeType = iota
ndString
ndInteger
ndSequence
ndIf
ndPrtc
ndPrts
ndPrti
ndWhile
ndAssign
ndNegate
ndNot
ndMul
ndDiv
ndMod
ndAdd
ndSub
ndLss
ndLeq
ndGtr
ndGeq
ndEql
ndNeq
ndAnd
ndOr
)
type tokS struct {
tok TokenType
errLn int
errCol int
text string // ident or string literal or integer value
}
type Tree struct {
nodeType NodeType
left *Tree
right *Tree
value string
}
// dependency: Ordered by tok, must remain in same order as TokenType consts
type atr struct {
text string
enumText string
tok TokenType
rightAssociative bool
isBinary bool
isUnary bool
precedence int
nodeType NodeType
}
var atrs = []atr{
{"EOI", "End_of_input", tkEOI, false, false, false, -1, -1},
{"*", "Op_multiply", tkMul, false, true, false, 13, ndMul},
{"/", "Op_divide", tkDiv, false, true, false, 13, ndDiv},
{"%", "Op_mod", tkMod, false, true, false, 13, ndMod},
{"+", "Op_add", tkAdd, false, true, false, 12, ndAdd},
{"-", "Op_subtract", tkSub, false, true, false, 12, ndSub},
{"-", "Op_negate", tkNegate, false, false, true, 14, ndNegate},
{"!", "Op_not", tkNot, false, false, true, 14, ndNot},
{"<", "Op_less", tkLss, false, true, false, 10, ndLss},
{"<=", "Op_lessequal", tkLeq, false, true, false, 10, ndLeq},
{">", "Op_greater", tkGtr, false, true, false, 10, ndGtr},
{">=", "Op_greaterequal", tkGeq, false, true, false, 10, ndGeq},
{"==", "Op_equal", tkEql, false, true, false, 9, ndEql},
{"!=", "Op_notequal", tkNeq, false, true, false, 9, ndNeq},
{"=", "Op_assign", tkAssign, false, false, false, -1, ndAssign},
{"&&", "Op_and", tkAnd, false, true, false, 5, ndAnd},
{"||", "Op_or", tkOr, false, true, false, 4, ndOr},
{"if", "Keyword_if", tkIf, false, false, false, -1, ndIf},
{"else", "Keyword_else", tkElse, false, false, false, -1, -1},
{"while", "Keyword_while", tkWhile, false, false, false, -1, ndWhile},
{"print", "Keyword_print", tkPrint, false, false, false, -1, -1},
{"putc", "Keyword_putc", tkPutc, false, false, false, -1, -1},
{"(", "LeftParen", tkLparen, false, false, false, -1, -1},
{")", "RightParen", tkRparen, false, false, false, -1, -1},
{"{", "LeftBrace", tkLbrace, false, false, false, -1, -1},
{"}", "RightBrace", tkRbrace, false, false, false, -1, -1},
{";", "Semicolon", tkSemi, false, false, false, -1, -1},
{",", "Comma", tkComma, false, false, false, -1, -1},
{"Ident", "Identifier", tkIdent, false, false, false, -1, ndIdent},
{"Integer literal", "Integer", tkInteger, false, false, false, -1, ndInteger},
{"String literal", "String", tkString, false, false, false, -1, ndString},
}
var displayNodes = []string{
"Identifier", "String", "Integer", "Sequence", "If", "Prtc", "Prts", "Prti",
"While", "Assign", "Negate", "Not", "Multiply", "Divide", "Mod", "Add",
"Subtract", "Less", "LessEqual", "Greater", "GreaterEqual", "Equal",
"NotEqual", "And", "Or",
}
var (
err error
token tokS
scanner *bufio.Scanner
)
func reportError(errLine, errCol int, msg string) {
log.Fatalf("(%d, %d) error : %s\n", errLine, errCol, msg)
}
func check(err error) {
if err != nil {
log.Fatal(err)
}
}
func getEum(name string) TokenType { // return internal version of name#
for _, atr := range atrs {
if atr.enumText == name {
return atr.tok
}
}
reportError(0, 0, fmt.Sprintf("Unknown token %s\n", name))
return tkEOI
}
func getTok() tokS {
tok := tokS{}
if scanner.Scan() {
line := strings.TrimRight(scanner.Text(), " \t")
fields := strings.Fields(line)
// [ ]*{lineno}[ ]+{colno}[ ]+token[ ]+optional
tok.errLn, err = strconv.Atoi(fields[0])
check(err)
tok.errCol, err = strconv.Atoi(fields[1])
check(err)
tok.tok = getEum(fields[2])
le := len(fields)
if le == 4 {
tok.text = fields[3]
} else if le > 4 {
idx := strings.Index(line, `"`)
tok.text = line[idx:]
}
}
check(scanner.Err())
return tok
}
func makeNode(nodeType NodeType, left *Tree, right *Tree) *Tree {
return &Tree{nodeType, left, right, ""}
}
func makeLeaf(nodeType NodeType, value string) *Tree {
return &Tree{nodeType, nil, nil, value}
}
func expect(msg string, s TokenType) {
if token.tok == s {
token = getTok()
return
}
reportError(token.errLn, token.errCol,
fmt.Sprintf("%s: Expecting '%s', found '%s'\n", msg, atrs[s].text, atrs[token.tok].text))
}
func expr(p int) *Tree {
var x, node *Tree
switch token.tok {
case tkLparen:
x = parenExpr()
case tkSub, tkAdd:
op := token.tok
token = getTok()
node = expr(atrs[tkNegate].precedence)
if op == tkSub {
x = makeNode(ndNegate, node, nil)
} else {
x = node
}
case tkNot:
token = getTok()
x = makeNode(ndNot, expr(atrs[tkNot].precedence), nil)
case tkIdent:
x = makeLeaf(ndIdent, token.text)
token = getTok()
case tkInteger:
x = makeLeaf(ndInteger, token.text)
token = getTok()
default:
reportError(token.errLn, token.errCol,
fmt.Sprintf("Expecting a primary, found: %s\n", atrs[token.tok].text))
}
for atrs[token.tok].isBinary && atrs[token.tok].precedence >= p {
op := token.tok
token = getTok()
q := atrs[op].precedence
if !atrs[op].rightAssociative {
q++
}
node = expr(q)
x = makeNode(atrs[op].nodeType, x, node)
}
return x
}
func parenExpr() *Tree {
expect("parenExpr", tkLparen)
t := expr(0)
expect("parenExpr", tkRparen)
return t
}
func stmt() *Tree {
var t, v, e, s, s2 *Tree
switch token.tok {
case tkIf:
token = getTok()
e = parenExpr()
s = stmt()
s2 = nil
if token.tok == tkElse {
token = getTok()
s2 = stmt()
}
t = makeNode(ndIf, e, makeNode(ndIf, s, s2))
case tkPutc:
token = getTok()
e = parenExpr()
t = makeNode(ndPrtc, e, nil)
expect("Putc", tkSemi)
case tkPrint: // print '(' expr {',' expr} ')'
token = getTok()
for expect("Print", tkLparen); ; expect("Print", tkComma) {
if token.tok == tkString {
e = makeNode(ndPrts, makeLeaf(ndString, token.text), nil)
token = getTok()
} else {
e = makeNode(ndPrti, expr(0), nil)
}
t = makeNode(ndSequence, t, e)
if token.tok != tkComma {
break
}
}
expect("Print", tkRparen)
expect("Print", tkSemi)
case tkSemi:
token = getTok()
case tkIdent:
v = makeLeaf(ndIdent, token.text)
token = getTok()
expect("assign", tkAssign)
e = expr(0)
t = makeNode(ndAssign, v, e)
expect("assign", tkSemi)
case tkWhile:
token = getTok()
e = parenExpr()
s = stmt()
t = makeNode(ndWhile, e, s)
case tkLbrace: // {stmt}
for expect("Lbrace", tkLbrace); token.tok != tkRbrace && token.tok != tkEOI; {
t = makeNode(ndSequence, t, stmt())
}
expect("Lbrace", tkRbrace)
case tkEOI:
// do nothing
default:
reportError(token.errLn, token.errCol,
fmt.Sprintf("expecting start of statement, found '%s'\n", atrs[token.tok].text))
}
return t
}
func parse() *Tree {
var t *Tree
token = getTok()
for {
t = makeNode(ndSequence, t, stmt())
if t == nil || token.tok == tkEOI {
break
}
}
return t
}
func prtAst(t *Tree) {
if t == nil {
fmt.Print(";\n")
} else {
fmt.Printf("%-14s ", displayNodes[t.nodeType])
if t.nodeType == ndIdent || t.nodeType == ndInteger || t.nodeType == ndString {
fmt.Printf("%s\n", t.value)
} else {
fmt.Println()
prtAst(t.left)
prtAst(t.right)
}
}
}
func main() {
source, err := os.Open("source.txt")
check(err)
defer source.Close()
scanner = bufio.NewScanner(source)
prtAst(parse())
}
输出：
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier count
Integer 1
Assign
Identifier n
Integer 1
Assign
Identifier limit
Integer 100
While
Less
Identifier n
Identifier limit
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier k
Integer 3
Assign
Identifier p
Integer 1
Assign
Identifier n
Add
Identifier n
Integer 2
While
And
LessEqual
Multiply
Identifier k
Identifier k
Identifier n
Identifier p
Sequence
Sequence
;
Assign
Identifier p
NotEqual
Multiply
Divide
Identifier n
Identifier k
Identifier k
Identifier n
Assign
Identifier k
Add
Identifier k
Integer 2
If
Identifier p
If
Sequence
Sequence
;
Sequence
Sequence
;
Prti
Identifier n
;
Prts
String " is prime\n"
;
Assign
Identifier count
Add
Identifier count
Integer 1
;
Sequence
Sequence
Sequence
;
Prts
String "Total primes found: "
;
Prti
Identifier count
;
Prts
String "\n"
;
