refactor: remove unused SymbolTable, keep Levenshtein

SymbolTable was built for scope tracking and "did you
mean?" suggestions but never integrated into the
interpreter. Levenshtein is used in env.go for fuzzy
matching, so move it to fuzzy.go where it belongs.

If we need a symbol table later, we can rebuild it
with the actual requirements in hand.

Author: amterp

core/fuzzy.go

@@ -5,6 +5,44 @@ import (
 	"unicode/utf8"
 )
 
+// Levenshtein calculates the Levenshtein distance between two strings.
+// Used for "did you mean?" suggestions.
+func Levenshtein(a, b string) int {
+	if len(a) == 0 {
+		return len(b)
+	}
+	if len(b) == 0 {
+		return len(a)
+	}
+
+	// Create matrix
+	matrix := make([][]int, len(a)+1)
+	for i := range matrix {
+		matrix[i] = make([]int, len(b)+1)
+		matrix[i][0] = i
+	}
+	for j := 0; j <= len(b); j++ {
+		matrix[0][j] = j
+	}
+
+	// Fill matrix
+	for i := 1; i <= len(a); i++ {
+		for j := 1; j <= len(b); j++ {
+			cost := 0
+			if a[i-1] != b[j-1] {
+				cost = 1
+			}
+			matrix[i][j] = min(
+				matrix[i-1][j]+1,      // deletion
+				matrix[i][j-1]+1,      // insertion
+				matrix[i-1][j-1]+cost, // substitution
+			)
+		}
+	}
+
+	return matrix[len(a)][len(b)]
+}
+
 // FuzzyMatchFold returns true if each character in source can be found in
 // target in order, using case-insensitive matching. This is a simplified
 // fuzzy search - not Levenshtein distance.

core/fuzzy_test.go

@@ -1,6 +1,10 @@
 package core
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
 
 func TestFuzzyMatchFold(t *testing.T) {
 	tests := []struct {
@@ -45,3 +49,25 @@ func TestFuzzyMatchFold(t *testing.T) {
 		})
 	}
 }
+
+func TestLevenshtein(t *testing.T) {
+	tests := []struct {
+		a, b     string
+		expected int
+	}{
+		{"", "", 0},
+		{"a", "", 1},
+		{"", "a", 1},
+		{"abc", "abc", 0},
+		{"abc", "abd", 1},
+		{"abc", "ab", 1},
+		{"abc", "abcd", 1},
+		{"kitten", "sitting", 3},
+		{"foobar", "foobaz", 1},
+	}
+
+	for _, tc := range tests {
+		result := Levenshtein(tc.a, tc.b)
+		assert.Equal(t, tc.expected, result, "Levenshtein(%q, %q)", tc.a, tc.b)
+	}
+}