From 97b616176598e1d68f261f354ce4de60008a422f Mon Sep 17 00:00:00 2001
From: Charlie Stanton <charlie@shtanton.xyz>
Date: Sun, 5 Mar 2023 08:39:12 +0000
Subject: Refactors out terminator literal stuff into a separate parsing
 function

---
 subex/parse.go | 154 ++++++++++++++-------------------------------------------
 1 file changed, 37 insertions(+), 117 deletions(-)

diff --git a/subex/parse.go b/subex/parse.go
index db07567..59b784d 100644
--- a/subex/parse.go
+++ b/subex/parse.go
@@ -4,9 +4,33 @@ import (
 	"main/walk"
 )
 
+func expectBracket(l *RuneReader, ifLeft walk.Datum, ifRight walk.Datum) walk.Datum {
+	switch l.next() {
+		case '(':
+			return ifLeft
+		case ')':
+			return ifRight
+		default:
+			panic("Expected ( or )")
+	}
+}
+
+// Having just read termType, read in a bracket and return the corresponding walk.Datum
+func parseTerminatorDatumLiteral(termType rune, l *RuneReader) walk.Datum {
+	switch termType {
+		case '@':
+			return expectBracket(l, walk.ArrayBegin, walk.ArrayEnd)
+		case '~':
+			return expectBracket(l, walk.StartString{}, walk.EndString{})
+		case '#':
+			return expectBracket(l, walk.MapBegin, walk.MapEnd)
+		default:
+			return nil
+	}
+}
+
 func parseReplacement(l *RuneReader) (output []TransducerOutput) {
 	// TODO escaping
-	// TODO refactor all the terminator stuff @, #, ~
 	loop: for {
 		r := l.next()
 		switch r {
@@ -20,33 +44,8 @@ func parseReplacement(l *RuneReader) (output []TransducerOutput) {
 					panic("Missing slot character")
 				}
 				output = append(output, TransducerReplacementLoad{datum: slot})
-			case '@':
-				terminal := l.next()
-				if terminal == '(' {
-					output = append(output, TransducerReplacementRune{datum: walk.ArrayBegin})
-				} else if terminal == ')' {
-					output = append(output, TransducerReplacementRune{datum: walk.ArrayEnd})
-				} else {
-					panic("Expected ( or ) after @")
-				}
-			case '~':
-				terminal := l.next()
-				if terminal == '(' {
-					output = append(output, TransducerReplacementRune{datum: walk.StartString{}})
-				} else if terminal == ')' {
-					output = append(output, TransducerReplacementRune{datum: walk.EndString{}})
-				} else {
-					panic("Expected ( or ) after ~")
-				}
-			case '#':
-				terminal := l.next()
-				if terminal == '(' {
-					output = append(output, TransducerReplacementRune{datum: walk.MapBegin})
-				} else if terminal == ')' {
-					output = append(output, TransducerReplacementRune{datum: walk.MapEnd})
-				} else {
-					panic("Expected ( or ) after #")
-				}
+			case '@', '~', '#':
+				output = append(output, TransducerReplacementRune{datum: parseTerminatorDatumLiteral(r, l)})
 			default:
 				output = append(output, TransducerReplacementRune{datum: r})
 		}
@@ -68,38 +67,11 @@ func parseRangeSubex(l *RuneReader) map[walk.Datum]walk.Datum {
 		} else if fromsStart == '=' {
 			hasTo = true
 			break
-		} else if fromsStart == '@' {
-			terminal := l.next()
-			if terminal == '(' {
-				froms = append(froms, walk.ArrayBegin)
-				continue
-			} else if terminal == ')' {
-				froms = append(froms, walk.ArrayEnd)
-				continue
-			} else {
-				panic("Expected ( or ) after @")
-			}
-		} else if fromsStart == '#' {
-			terminal := l.next()
-			if terminal == '(' {
-				froms = append(froms, walk.MapBegin)
-				continue
-			} else if terminal == ')' {
-				froms = append(froms, walk.MapEnd)
-				continue
-			} else {
-				panic("Expected ( or ) after #")
-			}
-		} else if fromsStart == '~' {
-			terminal := l.next()
-			if terminal == '(' {
-				froms = append(froms, walk.StartString{})
-				continue
-			} else if terminal == ')' {
-				froms = append(froms, walk.EndString{})
+		} else {
+			datum := parseTerminatorDatumLiteral(fromsStart, l)
+			if datum != nil {
+				froms = append(froms, datum)
 				continue
-			} else {
-				panic("Expected ( or ) after ~")
 			}
 		}
 		if l.accept("-") {
@@ -125,38 +97,11 @@ func parseRangeSubex(l *RuneReader) map[walk.Datum]walk.Datum {
 			tosStart := l.next()
 			if tosStart == ']' {
 				break
-			} else if tosStart == '@' {
-				terminal := l.next()
-				if terminal == '(' {
-					tos = append(tos, walk.ArrayBegin)
-					continue
-				} else if terminal == ')' {
-					tos = append(tos, walk.ArrayEnd)
-					continue
-				} else {
-					panic("Expected ( or ) after @")
-				}
-			} else if tosStart == '#' {
-				terminal := l.next()
-				if terminal == '(' {
-					tos = append(tos, walk.MapBegin)
-					continue
-				} else if terminal == ')' {
-					tos = append(tos, walk.MapEnd)
-					continue
-				} else {
-					panic("Expected ( or ) after #")
-				}
-			} else if tosStart == '~' {
-				terminal := l.next()
-				if terminal == '(' {
-					tos = append(tos, walk.StartString{})
-					continue
-				} else if terminal == ')' {
-					tos = append(tos, walk.EndString{})
+			} else {
+				datum := parseTerminatorDatumLiteral(tosStart, l)
+				if datum != nil {
+					tos = append(tos, datum)
 					continue
-				} else {
-					panic("Expected ( or ) after ~")
 				}
 			}
 			if l.accept("-") {
@@ -220,33 +165,8 @@ func parseSubex(l *RuneReader, minPower int) SubexAST {
 			lhs = SubexASTOutput{replacement}
 		case '.':
 			lhs = SubexASTCopyAny{}
-		case '@':
-			terminal := l.next()
-			if terminal == '(' {
-				lhs = SubexASTCopyRune{datum: walk.ArrayBegin}
-			} else if terminal == ')' {
-				lhs = SubexASTCopyRune{datum: walk.ArrayEnd}
-			} else {
-				panic("Expected ( or ) after @")
-			}
-		case '~':
-			terminal := l.next()
-			if terminal == '(' {
-				lhs = SubexASTCopyRune{datum: walk.StartString{}}
-			} else if terminal == ')' {
-				lhs = SubexASTCopyRune{datum: walk.EndString{}}
-			} else {
-				panic("Expected ( or ) after ~")
-			}
-		case '#':
-			terminal := l.next()
-			if terminal == '(' {
-				lhs = SubexASTCopyRune{datum: walk.MapBegin}
-			} else if terminal == ')' {
-				lhs = SubexASTCopyRune{datum: walk.MapEnd}
-			} else {
-				panic("Expected ( or ) after #")
-			}
+		case '@', '#', '~':
+			lhs = SubexASTCopyRune{datum: parseTerminatorDatumLiteral(r, l)}
 		default:
 			lhs = SubexASTCopyRune{datum: r}
 	}
-- 
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