From 0a8690993d572a50b95dd4f1c1903ed00ddb9c2b Mon Sep 17 00:00:00 2001
From: Charlie Stanton <charlie@shtanton.xyz>
Date: Wed, 21 Sep 2022 21:05:34 +0100
Subject: Initial commit

Parses and executes substitute expressions (subexes)

So far subex has the following operations:
- Concatenation of a and b with ab
- Or with |
- Repeat maximally with *
- Repeat minimally with -
- Copy a specific character 'a'
- Copy any character '.'
- Store text matching a regex into slot 's': `$s(regex)`
- Output text in "" including loading from slots with '$'

Regexes support all the same operations as subexes minus storing and outputting

This first implementation gives very little thought to efficiency

Example:

./main 'according to all known laws of aviation' '$1(.-)$m(( .* )| ).*"$m$1"'

This swaps the first and last words of the input string
---
 main/regexstate.go | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 main/regexstate.go

(limited to 'main/regexstate.go')

diff --git a/main/regexstate.go b/main/regexstate.go
new file mode 100644
index 0000000..16d5581
--- /dev/null
+++ b/main/regexstate.go
@@ -0,0 +1,48 @@
+package main
+
+type RegexState interface {
+	eat(char rune) []RegexState
+	accepting() bool
+}
+
+type RegexNoneState struct {}
+func (state RegexNoneState) eat(char rune) []RegexState {
+	return nil
+}
+func (state RegexNoneState) accepting() bool {
+	return true
+}
+
+type RegexAnyState struct {
+	next RegexState
+}
+func (state RegexAnyState) eat(char rune) []RegexState {
+	return []RegexState{state.next}
+}
+func (state RegexAnyState) accepting() bool {
+	return false
+}
+
+type RegexRuneState struct {
+	rune rune
+	next RegexState
+}
+func (state RegexRuneState) eat(char rune) []RegexState {
+	if char == state.rune {
+		return []RegexState{state.next}
+	}
+	return nil
+}
+func (state RegexRuneState) accepting() bool {
+	return false
+}
+
+type RegexGroupState struct {
+	first, second RegexState
+}
+func (state RegexGroupState) eat(char rune) []RegexState {
+	return append(state.first.eat(char), state.second.eat(char)...)
+}
+func (state RegexGroupState) accepting() bool {
+	return state.first.accepting() || state.second.accepting()
+}
-- 
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