new command gotry.

An exercise in reflection and an unusual tool.

From the usage message:

usage: gotry [packagedirectory] expression ...
Given one expression, gotry attempts to evaluate that expression.
Given multiple expressions, gotry treats them as a list of arguments
and result values and attempts to find a function in the package
that, given the first few expressions as arguments, evaluates to
the remaining expressions as results.  If the first expression has
methods, it will also search for applicable methods.

If there are multiple expressions, a package directory must be
specified. If there is a package argument, the expressions are
evaluated in an environment that includes
	import . "packagedirectory"

Examples:
	gotry 3+4
		# evaluates to 7
	gotry strings '"abc"' '"c"' 7-5
		# finds strings.Index etc.
	gotry regexp 'MustCompile("^[0-9]+")' '"12345"' true
		# finds Regexp.MatchString

R=rsc, PeterGo, r2
CC=golang-dev
https://golang.org/cl/2352043

src/cmd/gotest/Makefile

@@ -1,16 +1,18 @@
-# Copyright 2009 The Go Authors. All rights reserved.
+# 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.
 
 include ../../Make.inc
 
-TARG=gotest
+TARG=install
 
 clean:
 	@true
 
-install: $(TARG)
-	! test -f "$(GOBIN)"/$(TARG) || chmod u+w "$(GOBIN)"/$(TARG)
-	sed 's`@@GOROOT@@`$(GOROOT_FINAL)`' gotest >"$(GOBIN)"/$(TARG)
-	chmod +x "$(GOBIN)"/$(TARG)
+install: install-gotest install-gotry
+
+install-%: %
+	! test -f "$(GOBIN)"/$* || chmod u+w "$(GOBIN)"/$*
+	sed 's`@@GOROOT@@`$(GOROOT_FINAL)`' $* >"$(GOBIN)"/$*
+	chmod +x "$(GOBIN)"/$*
 

src/cmd/gotest/gotry

@@ -0,0 +1,167 @@
+#!/usr/bin/env bash
+# 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.
+
+# Using all the non-test *.go files in the named directory, write
+# out a file /tmp/$USER.try.go to evaluate the expressions on the
+# command line, perhaps to discover a function or method that
+# gives the desired results.  See usage message.
+# Compile the program and run it.
+
+# Makes egrep,grep work better in general if we put them
+# in ordinary C mode instead of what the current language is.
+unset LANG
+export LC_ALL=C
+export LC_CTYPE=C
+
+export GOROOT=${GOROOT:-"@@GOROOT@@"}
+eval $(gomake -j1 --no-print-directory -f "$GOROOT"/src/Make.inc go-env)
+if [ -z "$O" ]; then
+	echo 'missing $O - maybe no Make.$GOARCH?' 1>&2
+	exit 2
+fi
+
+# Allow overrides
+GC="${_GC:-$GC} -I _test"
+GL="${GL:-$LD} -L _test"
+AS="$AS"
+CC="$CC"
+LD="$LD"
+export GC GL O AS CC LD
+
+# Macros for tab and quotes for easier readability.
+T='	'
+BQ='`'
+SQ="'"
+DQ='"'
+SD="$SQ$DQ"
+DS="$DQ$SQ"
+
+usage="usage: gotry [packagedirectory] expression ...
+Given one expression, gotry attempts to evaluate that expression.
+Given multiple expressions, gotry treats them as a list of arguments
+and result values and attempts to find a function in the package
+that, given the first few expressions as arguments, evaluates to
+the remaining expressions as results.  If the first expression has
+methods, it will also search for applicable methods.
+
+If there are multiple expressions, a package directory must be
+specified. If there is a package argument, the expressions are
+evaluated in an environment that includes
+	import . ${DQ}packagedirectory${DQ}
+
+Examples:
+	gotry 3+4
+		# evaluates to 7
+	gotry strings ${SD}abc${DS} ${SD}c${DS} 7-5
+		# finds strings.Index etc.
+	gotry regexp ${SQ}MustCompile(${DQ}^[0-9]+${DQ})${SQ} ${SD}12345${DS} true
+		# finds Regexp.MatchString
+
+"
+
+function fail() {
+	echo 2>&1 "$@"
+	exit 2
+}
+
+case $# in
+	0)
+		fail "$usage"
+		;;
+	*)
+		case "$1" in
+		-*help|-*'?'|'?')
+			fail "$usage"
+		esac
+		if test -d "$GOROOT/src/pkg/$1"
+		then
+			pkg=$(basename $1)
+			dir=$GOROOT/src/pkg/$1
+			importdir=$1
+			shift
+			case "$pkg" in
+			os|syscall)
+				fail "gotry: cannot try packages os or syscall; they are too dangerous"
+			esac
+		fi
+		;;
+esac
+
+spaces='[ 	][ 	]*'
+
+function getFunctions() {
+	if [ "$pkg" = "" ]
+	then
+		return
+	fi
+	for file in $dir/*.go
+	do
+		case $file in
+		*_test*)
+			continue
+		esac
+		grep "func$spaces[A-Z]" $file | # TODO: should be Unicode upper case
+			sed "s/func$spaces//;s/(.*//"
+	done | sort -u
+}
+
+# Generate list of public functions.
+functions=$(getFunctions)
+
+# Write file to compile
+rm -f /tmp/$USER.try.go
+(
+cat <<'!'
+package main
+
+import (
+	"os"
+	"try"
+!
+
+if [ "$pkg" != "" ]
+then
+	echo "$T" . '"'$importdir'"'
+fi
+
+cat <<!
+)
+func main() {
+	try.Main("$pkg", firstArg, functions, args)
+}
+var functions = map[string] interface{}{
+!
+
+for i in $functions
+do
+	echo "$T"'"'$i'": '$i','
+done
+echo "}"
+
+echo 'var args = []interface{}{'
+
+if [ $# = 1 ]
+then
+	echo "${T}toSlice($1)",
+else
+for i
+	do
+		echo "$T$i",
+	done
+fi
+echo "}"
+
+cat <<!
+var firstArg = $BQ$1$BQ
+var _ os.Error
+func toSlice(a ...interface{}) []interface{} { return a }
+!
+
+)>/tmp/$USER.try.go
+
+$GC -o /tmp/$USER.try.$O /tmp/$USER.try.go &&
+$GL -o /tmp/$USER.try /tmp/$USER.try.$O &&
+/tmp/$USER.try "_$@"
+rm -f /tmp/$USER.try /tmp/$USER.try.go /tmp/$USER.try.$O

src/pkg/Makefile

@@ -123,6 +123,7 @@ DIRS=\
 	testing/quick\
 	testing/script\
 	time\
+	try\
 	unicode\
 	utf16\
 	utf8\
@@ -153,6 +154,7 @@ NOTEST=\
 	runtime/pprof\
 	syscall\
 	testing/iotest\
+	try\
 	../libcgo\
 	../cmd/cgo\
 	../cmd/ebnflint\

src/pkg/try/Makefile

@@ -0,0 +1,11 @@
+# Copyright 2009 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.
+
+include ../../Make.inc
+
+TARG=try
+GOFILES=\
+	try.go\
+
+include ../../Make.pkg

src/pkg/try/try.go

@@ -0,0 +1,174 @@
+// 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 try contains the executable part of the gotry command.
+// It is not intended for general use.
+package try
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"unicode"
+)
+
+var output io.Writer = os.Stdout // redirected when testing
+
+// Main is called directly from the gotry-generated Go source file to perform
+// the evaluations.
+func Main(pkg, firstArg string, functions map[string]interface{}, args []interface{}) {
+	switch len(args) {
+	case 0:
+		// Nothing to do.
+	case 1:
+		// Compiler has already evaluated the expression; just print the result.
+		printSlice(firstArg, args)
+	default:
+		// See if methods satisfy the expressions.
+		tryMethods(pkg, firstArg, args)
+		// See if functions satisfy the expressions.
+		for name, fn := range functions {
+			tryFunction(pkg, name, fn, args)
+		}
+	}
+}
+
+// printSlice prints the zeroth element of the args slice, which should (by construction)
+// itself be a slice of interface{}.
+func printSlice(firstArg string, args []interface{}) {
+	// Args should be length 1 and a slice.
+	if len(args) != 1 {
+		return
+	}
+	arg, ok := args[0].([]interface{})
+	if !ok {
+		return
+	}
+	fmt.Fprintf(output, "%s = ", firstArg)
+	if len(arg) > 1 {
+		fmt.Fprint(output, "(")
+	}
+	for i, a := range arg {
+		if i > 0 {
+			fmt.Fprint(output, ", ")
+		}
+		fmt.Fprintf(output, "%#v", a)
+	}
+	if len(arg) > 1 {
+		fmt.Fprint(output, ")")
+	}
+	fmt.Fprint(output, "\n")
+}
+
+// tryMethods sees if the zeroth arg has methods, and if so treats them as potential
+// functions to satisfy the remaining arguments.
+func tryMethods(pkg, firstArg string, args []interface{}) {
+	defer func() { recover() }()
+	// Is the first argument something with methods?
+	v := reflect.NewValue(args[0])
+	typ := v.Type()
+	if typ.NumMethod() == 0 {
+		return
+	}
+	for i := 0; i < typ.NumMethod(); i++ {
+		if unicode.IsUpper(int(typ.Method(i).Name[0])) {
+			tryMethod(pkg, firstArg, typ.Method(i), args)
+		}
+	}
+}
+
+// tryMethod converts a method to a function for tryOneFunction.
+func tryMethod(pkg, firstArg string, method reflect.Method, args []interface{}) {
+	rfn := method.Func
+	typ := method.Type
+	name := method.Name
+	tryOneFunction(pkg, firstArg, name, typ, rfn, args)
+}
+
+// tryFunction sees if fn satisfies the arguments.
+func tryFunction(pkg, name string, fn interface{}, args []interface{}) {
+	defer func() { recover() }()
+	rfn := reflect.NewValue(fn).(*reflect.FuncValue)
+	typ := rfn.Type().(*reflect.FuncType)
+	tryOneFunction(pkg, "", name, typ, rfn, args)
+}
+
+// tryOneFunction is the common code for tryMethod and tryFunction.
+func tryOneFunction(pkg, firstArg, name string, typ *reflect.FuncType, rfn *reflect.FuncValue, args []interface{}) {
+	// Any results?
+	if typ.NumOut() == 0 {
+		return // Nothing to do.
+	}
+	// Right number of arguments + results?
+	if typ.NumIn()+typ.NumOut() != len(args) {
+		return
+	}
+	// Right argument and result types?
+	for i, a := range args {
+		if i < typ.NumIn() {
+			if !compatible(a, typ.In(i)) {
+				return
+			}
+		} else {
+			if !compatible(a, typ.Out(i-typ.NumIn())) {
+				return
+			}
+		}
+	}
+	// Build the call args.
+	argsVal := make([]reflect.Value, typ.NumIn()+typ.NumOut())
+	for i, a := range args {
+		argsVal[i] = reflect.NewValue(a)
+	}
+	// Call the function and see if the results are as expected.
+	resultVal := rfn.Call(argsVal[:typ.NumIn()])
+	for i, v := range resultVal {
+		if !reflect.DeepEqual(v.Interface(), args[i+typ.NumIn()]) {
+			return
+		}
+	}
+	// Present the result including a godoc command to get more information.
+	firstIndex := 0
+	if firstArg != "" {
+		fmt.Fprintf(output, "%s.%s(", firstArg, name)
+		firstIndex = 1
+	} else {
+		fmt.Fprintf(output, "%s.%s(", pkg, name)
+	}
+	for i := firstIndex; i < typ.NumIn(); i++ {
+		if i > firstIndex {
+			fmt.Fprint(output, ", ")
+		}
+		fmt.Fprintf(output, "%#v", args[i])
+	}
+	fmt.Fprint(output, ") = ")
+	if typ.NumOut() > 1 {
+		fmt.Fprint(output, "(")
+	}
+	for i := 0; i < typ.NumOut(); i++ {
+		if i > 0 {
+			fmt.Fprint(output, ", ")
+		}
+		fmt.Fprintf(output, "%#v", resultVal[i].Interface())
+	}
+	if typ.NumOut() > 1 {
+		fmt.Fprint(output, ")")
+	}
+	fmt.Fprintf(output, "  // godoc %s %s\n", pkg, name)
+}
+
+// compatible reports whether the argument is compatible with the type.
+func compatible(arg interface{}, typ reflect.Type) bool {
+	if reflect.Typeof(arg) == typ {
+		return true
+	}
+	if arg == nil {
+		// nil is OK if the type is an interface.
+		if _, ok := typ.(*reflect.InterfaceType); ok {
+			return true
+		}
+	}
+	return false
+}

src/pkg/try/try_test.go

@@ -0,0 +1,60 @@
+// 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 try
+
+import (
+	"bytes"
+	"regexp" // Used as the package to try.
+	"testing"
+)
+
+// The global functions in package regexp at time of writing.
+// Doesn't need to be updated unless the entries in this list become invalid.
+var functions = map[string]interface{}{
+	"Compile":     regexp.Compile,
+	"Match":       regexp.Match,
+	"MatchString": regexp.MatchString,
+	"MustCompile": regexp.MustCompile,
+	"QuoteMeta":   regexp.QuoteMeta,
+}
+
+// A wraps arguments to make the test cases nicer to read.
+func A(args ...interface{}) []interface{} {
+	return args
+}
+
+type Test struct {
+	firstArg string // only needed if there is exactly one argument
+	result   string // minus final newline; might be just the godoc string
+	args     []interface{}
+}
+
+var testRE = regexp.MustCompile("a(.)(.)d")
+
+var tests = []Test{
+	// A simple expression.  The final value is a slice in case the expression is multivalue.
+	Test{"3+4", "3+4 = 7", A([]interface{}{7})},
+	// A search for a function.
+	Test{"", "regexp QuoteMeta", A("([])", `\(\[\]\)`)},
+	// A search for a function with multiple return values.
+	Test{"", "regexp MatchString", A("abc", "xabcd", true, nil)},
+	// Searches for methods.
+	Test{"", "regexp MatchString", A(testRE, "xabcde", true)},
+	Test{"", "regexp NumSubexp", A(testRE, 2)},
+}
+
+func TestAll(t *testing.T) {
+	re := regexp.MustCompile(".*// godoc ")
+	for _, test := range tests {
+		b := new(bytes.Buffer)
+		output = b
+		Main("regexp", test.firstArg, functions, test.args)
+		expect := test.result + "\n"
+		got := re.ReplaceAllString(b.String(), "")
+		if got != expect {
+			t.Errorf("expected %q; got %q", expect, got)
+		}
+	}
+}