From 5d8582711936cae3c42f2645d0f304418b17fb7e Mon Sep 17 00:00:00 2001
From: Charlie Stanton <charlie@shtanton.xyz>
Date: Fri, 21 Apr 2023 15:31:00 +0100
Subject: Replace implementation of Atomise to improve performance

---
 walk/walk.go | 45 +++++++++++++++++++++++++++++----------------
 1 file changed, 29 insertions(+), 16 deletions(-)

diff --git a/walk/walk.go b/walk/walk.go
index 6d00ef2..490a6f2 100644
--- a/walk/walk.go
+++ b/walk/walk.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"strings"
 	"math"
+	"unicode/utf8"
 )
 
 // int or string
@@ -48,8 +49,8 @@ const (
 	MapBegin
 	MapEnd
 )
-func (value TerminalValue) Atomise() []Atom {
-	return []Atom{value}
+func (value TerminalValue) Atomise(in []Atom) []Atom {
+	return append(in, value)
 }
 func (value TerminalValue) String() string {
 	switch value {
@@ -67,16 +68,16 @@ func (value TerminalValue) String() string {
 }
 
 type ValueNull struct {}
-func (value ValueNull) Atomise() []Atom {
-	return []Atom{ValueNull{}}
+func (value ValueNull) Atomise(in []Atom) []Atom {
+	return append(in, value)
 }
 func (value ValueNull) String() string {
 	return "null"
 }
 
 type ValueBool bool
-func (value ValueBool) Atomise() []Atom {
-	return []Atom{value}
+func (value ValueBool) Atomise(in []Atom) []Atom {
+	return append(in, value)
 }
 func (value ValueBool) String() string {
 	if value {
@@ -87,8 +88,8 @@ func (value ValueBool) String() string {
 }
 
 type ValueNumber float64
-func (value ValueNumber) Atomise() []Atom {
-	return []Atom{value}
+func (value ValueNumber) Atomise(in []Atom) []Atom {
+	return append(in, value)
 }
 func (value ValueNumber) String() string {
 	v := float64(value)
@@ -106,13 +107,13 @@ func (value StringAtom) String() string {
 }
 
 type ValueString string
-func (value ValueString) Atomise() (out []Atom) {
-	out = append(out, StringTerminal{})
+func (value ValueString) Atomise(in []Atom) []Atom {
+	in = append(in, StringTerminal{})
 	for _, char := range value {
-		out = append(out, StringAtom(char))
+		in = append(in, StringAtom(char))
 	}
-	out = append(out, StringTerminal{})
-	return out
+	in = append(in, StringTerminal{})
+	return in
 }
 func (value ValueString) String() string {
 	return fmt.Sprintf("\"%s\"", string(value))
@@ -123,7 +124,8 @@ type Atom interface {
 }
 
 type WalkValue interface {
-	Atomise() []Atom
+	// Append this values atoms to the input
+	Atomise(in []Atom) []Atom
 	String() string
 }
 
@@ -427,9 +429,20 @@ func ConcatData(first []Atom, second []Atom) []Atom {
 }
 
 func Atomise(in []WalkValue) (out []Atom) {
-	out = make([]Atom, 0, len(in) * 2)
+	numAtoms := 0
+	for _, value := range in {
+		switch v := value.(type) {
+			case TerminalValue, ValueNull, ValueBool, ValueNumber:
+				numAtoms++
+			case ValueString:
+				numAtoms += utf8.RuneCountInString(string(v)) + 2
+			default:
+				panic("Invalid WalkValue")
+		}
+	}
+	out = make([]Atom, 0, numAtoms)
 	for _, value := range in {
-		out = append(out, value.Atomise()...)
+		out = value.Atomise(out)
 	}
 	return out
 }
-- 
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