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/regexast.go | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 main/regexast.go

(limited to 'main/regexast.go')

diff --git a/main/regexast.go b/main/regexast.go
new file mode 100644
index 0000000..0aab053
--- /dev/null
+++ b/main/regexast.go
@@ -0,0 +1,72 @@
+package main
+
+import (
+	"fmt"
+)
+
+type RegexAST interface {
+	compileWith(next RegexState) RegexState
+}
+
+type RegexASTRune rune
+func (ast RegexASTRune) compileWith(next RegexState) RegexState {
+	return RegexRuneState{
+		rune: rune(ast),
+		next: next,
+	}
+}
+func (ast RegexASTRune) String() string {
+	return string(rune(ast))
+}
+
+type RegexASTAny struct {}
+func (ast RegexASTAny) compileWith(next RegexState) RegexState {
+	return RegexAnyState{next}
+}
+func (ast RegexASTAny) String() string {
+	return "."
+}
+
+type RegexASTConcat struct {
+	first, second RegexAST
+}
+func (ast RegexASTConcat) compileWith(next RegexState) RegexState {
+	return ast.first.compileWith(ast.second.compileWith(next))
+}
+func (ast RegexASTConcat) String() string {
+	return fmt.Sprintf("Concat{%v, %v}", ast.first, ast.second)
+}
+
+type RegexASTOr struct {
+	first, second RegexAST
+}
+func (ast RegexASTOr) compileWith(next RegexState) RegexState {
+	return RegexGroupState{
+		ast.first.compileWith(next),
+		ast.second.compileWith(next),
+	}
+}
+
+type RegexASTMaximise struct {
+	content RegexAST
+}
+func (ast RegexASTMaximise) compileWith(next RegexState) RegexState {
+	state := &RegexGroupState{
+		nil,
+		next,
+	}
+	state.first = ast.content.compileWith(state)
+	return state
+}
+
+type RegexASTMinimise struct {
+	content RegexAST
+}
+func (ast RegexASTMinimise) compileWith(next RegexState) RegexState {
+	state := &RegexGroupState{
+		next,
+		nil,
+	}
+	state.second = ast.content.compileWith(state)
+	return state
+}
-- 
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