From 3cb886859e9b4df4ece183583dfd8b5ba7a59584 Mon Sep 17 00:00:00 2001
From: Charlie Stanton <charlie@shtanton.xyz>
Date: Thu, 20 Apr 2023 16:57:48 +0100
Subject: Adds some shorthands for substituting the beginning and end of the
 path register

---
 main/lex.go   |  2 +-
 main/parse.go | 67 ++++++++++++++++++++++++++++++++++++++++++++++-------------
 2 files changed, 53 insertions(+), 16 deletions(-)

diff --git a/main/lex.go b/main/lex.go
index 2826b1e..ecb0d3d 100644
--- a/main/lex.go
+++ b/main/lex.go
@@ -179,7 +179,7 @@ func lexCommand(l *lexer) stateFunc {
 		case '}':
 			l.emit(TokenRBrace)
 			return lexCommand
-		case 's', 'S':
+		case 's', 'S', 'f', 'F', 'l', 'L':
 			l.emit(TokenCommand)
 			return lexSubstitution
 	}
diff --git a/main/parse.go b/main/parse.go
index 198b746..dc86fd6 100644
--- a/main/parse.go
+++ b/main/parse.go
@@ -33,7 +33,7 @@ func (p *parser) peek() Token {
 	return token
 }
 
-func (p *parser) parseSubex() subex.SubexState {
+func (p *parser) parseSubex() subex.SubexAST {
 	delim := p.next()
 	if delim.typ != TokenSubstituteDelimiter {
 		panic("Missing substitute delimiter")
@@ -50,12 +50,11 @@ func (p *parser) parseSubex() subex.SubexState {
 	}
 	reader := subex.NewStringRuneReader(subexProgram)
 	subexAST := subex.Parse(reader)
-	subex := subex.CompileTransducer(subexAST)
 	delim = p.next()
 	if delim.typ != TokenSubstituteDelimiter {
 		panic("Missing end substitute delimiter")
 	}
-	return subex
+	return subexAST
 }
 
 func (p *parser) parseBasicCommand(commandChar rune) Command {
@@ -70,8 +69,49 @@ func (p *parser) parseBasicCommand(commandChar rune) Command {
 			return NextCommand{}
 		case 'N':
 			return AppendNextCommand{}
-		case 's', 'S':
-			subex := p.parseSubex()
+		case 's', 'S', 'f', 'F', 'l', 'L':
+			ast := p.parseSubex()
+			switch commandChar {
+				case 'f':
+					ast = subex.SubexASTConcat {
+						First: ast,
+						Second: subex.SubexASTRepeat {
+							Content: subex.SubexASTCopyAny{},
+							Acceptable: []subex.ConvexRange{{Start: -1, End: 0}},
+						},
+					}
+				case 'F':
+					ast = subex.SubexASTConcat {
+						First: subex.SubexASTStore {
+							Slot: '_',
+							Match: ast,
+						},
+						Second: subex.SubexASTRepeat {
+							Content: subex.SubexASTCopyAny{},
+							Acceptable: []subex.ConvexRange{{Start: -1, End: 0}},
+						},
+					}
+				case 'l':
+					ast = subex.SubexASTConcat {
+						First: subex.SubexASTRepeat {
+							Content: subex.SubexASTCopyAny{},
+							Acceptable: []subex.ConvexRange{{Start: 0, End: -1}},
+						},
+						Second: ast,
+					}
+				case 'L':
+					ast = subex.SubexASTConcat {
+						First: subex.SubexASTRepeat {
+							Content: subex.SubexASTCopyAny{},
+							Acceptable: []subex.ConvexRange{{Start: 0, End: -1}},
+						},
+						Second: subex.SubexASTStore {
+							Slot: '_',
+							Match: ast,
+						},
+					}
+			}
+			subex := subex.CompileTransducer(ast)
 			var next Command
 			token := p.peek()
 			switch token.typ {
@@ -80,16 +120,13 @@ func (p *parser) parseBasicCommand(commandChar rune) Command {
 				default:
 					next = p.parseCommand()
 			}
-			if (commandChar == 's') {
-				return SubstituteValueCommand {
-					subex: subex,
-					next: next,
-				}
-			} else {
-				return SubstitutePathCommand {
-					subex: subex,
-					next: next,
-				}
+			switch commandChar {
+				case 's':
+					return SubstituteValueCommand {subex, next}
+				case 'S', 'f', 'F', 'l', 'L':
+					return SubstitutePathCommand {subex, next}
+				default:
+					panic("Unreachable!?!?")
 			}
 		case 'o':
 			return NoopCommand{}
-- 
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