From d3d17484012dc603ae326bec419cff990898e6a0 Mon Sep 17 00:00:00 2001
From: Charlie Stanton <charlie@shtanton.xyz>
Date: Wed, 19 Apr 2023 13:48:15 +0100
Subject: Adds the reciprocal operator

---
 subex/arithmetic.go | 34 ++++++++++++++++++++++++++++++++++
 subex/parse.go      |  2 ++
 subex/subexast.go   | 15 +++++++++++++++
 3 files changed, 51 insertions(+)

diff --git a/subex/arithmetic.go b/subex/arithmetic.go
index ff30a58..4404a1c 100644
--- a/subex/arithmetic.go
+++ b/subex/arithmetic.go
@@ -118,3 +118,37 @@ func negateValues(atoms []walk.Atom) ([]walk.Atom, error) {
 	}
 	return negatedNumbers, nil
 }
+
+// If all are castable to numbers, takes reciprocals of all and returns them
+// Else errors
+func reciprocalValues(atoms []walk.Atom) ([]walk.Atom, error) {
+	var reciprocals []walk.Atom
+	values, err := walk.MemoryCompound(atoms)
+	if err != nil {
+		return nil, err
+	}
+	for _, value := range values {
+		switch v := value.(type) {
+			case walk.ValueNull:
+				return nil, errors.New("Tried to take reciprocal of null")
+			case walk.ValueBool:
+				if bool(v) {
+					reciprocals = append(reciprocals, walk.ValueNumber(1))
+				} else {
+					return nil, errors.New("Tried to take reciprocal of false")
+				}
+			case walk.ValueNumber:
+				reciprocals = append(reciprocals, walk.ValueNumber(1 / v))
+			case walk.ValueString:
+				num, err := strconv.ParseFloat(string(v), 64)
+				if err == nil {
+					reciprocals = append(reciprocals, walk.ValueNumber(1 / num))
+				} else {
+					return nil, errors.New("Tried to take reciprocal of non-castable string")
+				}
+			default:
+				return nil, errors.New("Tried to take reciprocal of non-number")
+		}
+	}
+	return reciprocals, nil
+}
diff --git a/subex/parse.go b/subex/parse.go
index 8635186..f5316c9 100644
--- a/subex/parse.go
+++ b/subex/parse.go
@@ -240,6 +240,8 @@ func parseSubex(l *RuneReader, minPower int) SubexAST {
 				lhs = SubexASTProduct {lhs}
 			case r == '-' && minPower <= 8:
 				lhs = SubexASTNegate {lhs}
+			case r == '/' && minPower <= 8:
+				lhs = SubexASTReciprocal {lhs}
 			case r == '$' && minPower <= 8:
 				slot := l.next()
 				if slot == eof {
diff --git a/subex/subexast.go b/subex/subexast.go
index 3c807ee..78c9aff 100644
--- a/subex/subexast.go
+++ b/subex/subexast.go
@@ -223,3 +223,18 @@ func (ast SubexASTNegate) compileWith(next SubexState) SubexState {
 		}),
 	}
 }
+
+// Runs the content Subex and collects the output
+// If it is a list of atoms castable to numbers, it takes the reciprocal of them all and outputs them
+// Else it rejects
+type SubexASTReciprocal struct {
+	content SubexAST
+}
+func (ast SubexASTReciprocal) compileWith(next SubexState) SubexState {
+	return &SubexCaptureBeginState {
+		next: ast.content.compileWith(&SubexArithmeticEndState {
+			next: next,
+			calculate: reciprocalValues,
+		}),
+	}
+}
-- 
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