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Diffstat (limited to 'doc/talks/io2010/eval1.go')
| -rw-r--r-- | doc/talks/io2010/eval1.go | 227 |
1 files changed, 0 insertions, 227 deletions
diff --git a/doc/talks/io2010/eval1.go b/doc/talks/io2010/eval1.go deleted file mode 100644 index 582f43e8ea..0000000000 --- a/doc/talks/io2010/eval1.go +++ /dev/null @@ -1,227 +0,0 @@ -// Copyright 2010 The Go 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 main - -import ( - "bufio" - "fmt" - "os" - "strconv" - "strings" -) - -// Generic expression parser/evaluator - -type Value interface { - String() string - BinaryOp(op string, y Value) Value -} - -type Parser struct { - precTab map[string]int - newVal func(string) Value - src string - pos int - tok string -} - -const alphanum = "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" - -func (p *Parser) stop(c uint8) bool { - switch { - case p.pos >= len(p.src): - return true - case c == '"': - if p.src[p.pos] == '"' { - p.pos++ - return true - } - return false - case strings.IndexRune(alphanum, int(c)) >= 0: - return strings.IndexRune(alphanum, int(p.src[p.pos])) < 0 - } - return true -} - -func (p *Parser) next() { - // skip blanks - for ; p.pos < len(p.src) && p.src[p.pos] <= ' '; p.pos++ { - } - if p.pos >= len(p.src) { - p.tok = "" - return - } - start := p.pos - c := p.src[p.pos] - for p.pos < len(p.src) { - p.pos++ - if p.stop(c) { - break - } - } - p.tok = p.src[start:p.pos] -} - -func (p *Parser) binaryExpr(prec1 int) Value { - x := p.newVal(p.tok) - p.next() - for prec := p.precTab[p.tok]; prec >= prec1; prec-- { - for p.precTab[p.tok] == prec { - op := p.tok - p.next() - y := p.binaryExpr(prec + 1) - x = x.BinaryOp(op, y) - } - } - return x -} - -func Eval(precTab map[string]int, newVal func(string) Value, src string) Value { - var p Parser - p.precTab = precTab - p.newVal = newVal - p.src = src - p.next() - return p.binaryExpr(1) -} - -// Command-line expression evaluator - -func main() { - r := bufio.NewReader(os.Stdin) - for { - fmt.Printf("> ") - line, err := r.ReadString('\n') - if err != nil { - break - } - fmt.Printf("%s\n", Eval(precTab, trace(newVal), line)) - } -} - -// Custom grammar and values - -var precTab = map[string]int{ - "&&": 1, - "||": 2, - "==": 3, - "!=": 3, - "<": 3, - "<=": 3, - ">": 3, - ">=": 3, - "+": 4, - "-": 4, - "*": 5, - "/": 5, - "%": 5, -} - -func newVal(lit string) Value { - x, err := strconv.Atoi(lit) - if err == nil { - return Int(x) - } - b, err := strconv.ParseBool(lit) - if err == nil { - return Bool(b) - } - return Error(fmt.Sprintf("illegal literal '%s'", lit)) -} - -type Error string - -func (e Error) String() string { return string(e) } -func (e Error) BinaryOp(op string, y Value) Value { return e } - -type Int int - -func (x Int) String() string { return strconv.Itoa(int(x)) } -func (x Int) BinaryOp(op string, y Value) Value { - switch y := y.(type) { - case Error: - return y - case Int: - switch op { - case "+": - return x + y - case "-": - return x - y - case "*": - return x * y - case "/": - return x / y - case "%": - return x % y - case "==": - return Bool(x == y) - case "!=": - return Bool(x != y) - case "<": - return Bool(x < y) - case "<=": - return Bool(x <= y) - case ">": - return Bool(x > y) - case ">=": - return Bool(x >= y) - } - } - return Error(fmt.Sprintf("illegal operation: '%v %s %v'", x, op, y)) -} - -type Bool bool - -func (x Bool) String() string { return strconv.FormatBool(bool(x)) } -func (x Bool) BinaryOp(op string, y Value) Value { - switch y := y.(type) { - case Error: - return y - case Bool: - switch op { - case "&&": - return Bool(x && y) - case "||": - return Bool(x || y) - case "==": - return Bool(x == y) - case "!=": - return Bool(x != y) - } - } - return Error(fmt.Sprintf("illegal operation: '%v %s %v'", x, op, y)) -} - -func trace(newVal func(string) Value) func(string) Value { - return func(s string) Value { - v := newVal(s) - fmt.Printf("\tnewVal(%q) = %s\n", s, fmtv(v)) - return &traceValue{v} - } -} - -type traceValue struct { - Value -} - -func (x *traceValue) BinaryOp(op string, y Value) Value { - z := x.Value.BinaryOp(op, y.(*traceValue).Value) - fmt.Printf("\t%s.BinaryOp(%q, %s) = %s\n", fmtv(x.Value), op, fmtv(y.(*traceValue).Value), fmtv(z)) - return &traceValue{z} -} - -func (x *traceValue) String() string { - s := x.Value.String() - fmt.Printf("\t%s.String() = %#v\n", fmtv(x.Value), s) - return s -} - -func fmtv(v Value) string { - t := fmt.Sprintf("%T", v) - if i := strings.LastIndex(t, "."); i >= 0 { // strip package - t = t[i+1:] - } - return fmt.Sprintf("%s(%#v)", t, v) -} |