Remove a few allocs from Run

.gitignore

@@ -4,3 +4,4 @@
 cpu.out
 mem.out
 /vendor
+trace.log

errors.go

@@ -0,0 +1,26 @@
+package goparsify
+
+import "fmt"
+
+// Error represents a parse error. These will often be set, the parser will back up a little and
+// find another viable path. In general when combining errors the longest error should be returned.
+type Error struct {
+	pos      int
+	expected string
+}
+
+// Pos is the offset into the document the error was found
+func (e *Error) Pos() int { return e.pos }
+
+// Error satisfies the golang error interface
+func (e *Error) Error() string { return fmt.Sprintf("offset %d: expected %s", e.pos, e.expected) }
+
+// UnparsedInputError is returned by Run when not all of the input was consumed. There may still be a valid result
+type UnparsedInputError struct {
+	remaining string
+}
+
+// Error satisfies the golang error interface
+func (e UnparsedInputError) Error() string {
+	return "left unparsed: " + e.remaining
+}

parser.go

@@ -1,7 +1,6 @@
 package goparsify
 
 import (
-	"errors"
 	"fmt"
 	"regexp"
 	"strings"
@@ -90,11 +89,11 @@ func Run(parser Parserish, input string, ws ...VoidParser) (result interface{},
 	ps.AutoWS()
 
 	if ps.Error.expected != "" {
-		return ret.Result, ps.Error
+		return ret.Result, &ps.Error
 	}
 
 	if ps.Get() != "" {
-		return ret.Result, errors.New("left unparsed: " + ps.Get())
+		return ret.Result, UnparsedInputError{ps.Get()}
 	}
 
 	return ret.Result, nil

perf_test.go

@@ -5,6 +5,7 @@ import "testing"
 func BenchmarkAny(b *testing.B) {
 	p := Any("hello", "goodbye", "help")
 
+	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		_, _ = Run(p, "hello")
 		_, _ = Run(p, "hello world")

scripts/benchalloc.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+if [ $# != 1 ] ; then
+    echo Run this in a directory containing benchmarks and pass it the name of a benchmark. It will dump allocations out to trace.log
+    exit
+fi
+
+set -eu
+
+go test -c
+
+GODEBUG=allocfreetrace=1 ./$(basename $(pwd)).test.exe  -test.run=none -test.bench=$1 -test.benchmem -test.benchtime=1ns 2> >(sed -n '/benchmark.go:75/,$p' > trace.log)

state.go

@@ -1,24 +1,10 @@
 package goparsify
 
 import (
-	"fmt"
 	"unicode"
 	"unicode/utf8"
 )
 
-// Error represents a parse error. These will often be set, the parser will back up a little and
-// find another viable path. In general when combining errors the longest error should be returned.
-type Error struct {
-	pos      int
-	expected string
-}
-
-// Pos is the offset into the document the error was found
-func (e Error) Pos() int { return e.pos }
-
-// Error satisfies the golang error interface
-func (e Error) Error() string { return fmt.Sprintf("offset %d: expected %s", e.pos, e.expected) }
-
 // State is the current parse state. It is entirely public because parsers are expected to mutate it during the parse.
 type State struct {
 	// The full input string