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/main.go | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 main/main.go

(limited to 'main/main.go')

diff --git a/main/main.go b/main/main.go
new file mode 100644
index 0000000..be43d90
--- /dev/null
+++ b/main/main.go
@@ -0,0 +1,86 @@
+package main
+
+import (
+	"os"
+	"fmt"
+)
+
+type TransducerOutput interface {
+	build(Store) string
+}
+
+type TransducerReplacementRune rune
+func (replacement TransducerReplacementRune) build(store Store) string {
+	return string(replacement)
+}
+
+type TransducerReplacementLoad rune
+func (replacement TransducerReplacementLoad) build(store Store) string {
+	return store[rune(replacement)]
+}
+
+type Store map[rune]string
+func (store Store) clone() Store {
+	newStore := make(Store)
+	for key, val := range store {
+		newStore[key] = val
+	}
+	return newStore
+}
+
+func compileTransducer(transducerAst SubexAST) SubexState {
+	return transducerAst.compileWith(SubexNoneState{})
+}
+
+type SubexBranch struct {
+	store Store
+	state SubexState
+	output string
+}
+func (pair SubexBranch) eat(char rune) []SubexBranch {
+	states := pair.state.eat(pair.store, char)
+	for i := range states {
+		states[i].output = pair.output + states[i].output
+	}
+	return states
+}
+func (pair SubexBranch) accepting() []string {
+	return pair.state.accepting(pair.store)
+}
+
+func runTransducer(transducer SubexState, input string) (output string, err bool) {
+	states := []SubexBranch{{
+		state: transducer,
+		output: "",
+		store: make(Store),
+	}}
+	for _, char := range input {
+		var newStates []SubexBranch
+		for _, state := range states {
+			newStates = append(newStates, state.eat(char)...)
+		}
+		states = newStates
+	}
+	for _, state := range states {
+		outputEnds := state.accepting()
+		for _, outputEnd := range outputEnds {
+			return state.output + outputEnd, false
+		}
+	}
+	return "", true
+}
+
+func main() {
+	if len(os.Args) != 3 {
+		panic("Expected: program [input] [subex]")
+	}
+	input := os.Args[1]
+	program := os.Args[2]
+	ast := parse(program)
+	transducer := compileTransducer(ast)
+	output, err := runTransducer(transducer, input)
+	if err {
+		output = input
+	}
+	fmt.Println(output)
+}
-- 
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