style: renamed samples to tests

Changed 'lambda' to '/lambda' in .gitignore to prevent accidentally
hiding files in pkg/lambda/ directory. The pattern now correctly
excludes only the compiled binary at the repository root.

Also adds previously hidden pkg/lambda/iterator.go to the repository.

.gitignore

@@ -3,7 +3,7 @@
 # https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
 #
 # Binaries for programs and plugins
-lambda
+/lambda
 *.exe
 *.exe~
 *.dll

cmd/lambda/benchmark_test.go

@@ -51,11 +51,11 @@ func runSample(samplePath string) error {
 // Benchmark all samples using sub-benchmarks.
 func BenchmarkSamples(b *testing.B) {
 	samples := map[string]string{
-		"Church":     "../../samples/church.txt",
+		"Church":     "../../samples/church.test",
-		"Fast":       "../../samples/fast.txt",
+		"Fast":       "../../samples/fast.test",
-		"Saccharine": "../../samples/saccharine.txt",
+		"Saccharine": "../../samples/saccharine.test",
-		"Simple":     "../../samples/simple.txt",
+		"Simple":     "../../samples/simple.test",
-		"Thunk":      "../../samples/thunk.txt",
+		"Thunk":      "../../samples/thunk.test",
 	}
 
 	for name, path := range samples {

pkg/lambda/iterator.go

@@ -0,0 +1,59 @@
+package lambda
+
+type Iterator struct {
+	trace []*Expression
+}
+
+func NewIterator(expr *Expression) *Iterator {
+	return &Iterator{
+		trace: []*Expression{expr},
+	}
+}
+
+func (i *Iterator) Current() *Expression {
+	if len(i.trace) < 1 {
+		return nil
+	}
+
+	return i.trace[len(i.trace)-1]
+}
+
+func (i *Iterator) Parent() *Expression {
+	if len(i.trace) < 2 {
+		return nil
+	}
+
+	return i.trace[len(i.trace)-2]
+}
+
+func (i *Iterator) Next() {
+	switch typed := (*i.Current()).(type) {
+	case *Abstraction:
+		i.trace = append(i.trace, &typed.body)
+	case *Application:
+		i.trace = append(i.trace, &typed.abstraction)
+	case *Variable:
+		for len(i.trace) > 1 {
+			if app, ok := (*i.Parent()).(*Application); ok {
+				if app.abstraction == *i.Current() {
+					i.Back()
+					i.trace = append(i.trace, &app.argument)
+					return
+				}
+			}
+
+			i.Back()
+		}
+
+		i.trace = []*Expression{}
+	}
+}
+
+func (i *Iterator) Back() bool {
+	if len(i.trace) == 0 {
+		return false
+	}
+
+	i.trace = i.trace[:len(i.trace)-1]
+	return true
+}

samples/church.txt

@@ -1,7 +0,0 @@
-0 := \f.\x.x
-inc n := \f x.(f (n f x))
-exp n m := (m n)
-
-N := (inc (inc (inc (inc (inc (inc 0))))))
-
-(exp N N)

samples/fast.txt

@@ -1,11 +0,0 @@
-fix f := (\x.(f (x x)) \x.(f (x x)))
-
-inc := (fix \self.\l.(((l \x.\y.x) ((((l \x.\y.y) \x.\y.x) \c.((c \x.\y.x) \c.((c \x.\y.y) (self ((l \x.\y.y) \x.\y.y))))) \c.((c \x.\y.x) \c.((c \x.\y.x) ((l \x.\y.y) \x.\y.y))))) \c.((c \x.\y.x) \c.((c \x.\y.x) \VAR0.\x.\y.y))))
-one := \c.((c \x.\y.x) \c.((c \x.\y.x) \VAR0.\x.\y.y))
-double := \N.\c.((c \x.\y.x) \c.((c \x.\y.y) N))
-print := (fix \self.\l.(((l \x.\y.x) (((((l \x.\y.y) \x.\y.x) 1) 0) (self ((l \x.\y.y) \x.\y.y)))) END))
-
-
-N := \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.y) \c.((c \x.\y.x) \c.((c \x.\y.x) \VAR0.\x.\y.y))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
-
-(print N)

samples/saccharine.txt

@@ -1,52 +0,0 @@
-T x y := x
-F x y := y
-if b t e := (b t e)
-
-pair a b := \c.(c a b)
-left p := (p T)
-right p := (p F)
-
-print n := (n 0 1 end)
-
-fix f := (\x.(f (x x)) \x.(f (x x)))
-
-some x := (pair T x)
-none := \.F
-isfull := left
-unwrap := right
-
-nil := none
-push i l := (some (pair i l))
-peek l := (left (unwrap l))
-pop l := (right (unwrap l))
- 
-inc := (fix \self l.{
-  (if (isfull l)
-    (if (peek l)
-      (push F (self (pop l)))
-      (push T (pop l))
-    )
-    (push T nil)
-  )
-})
-
-print := (fix \self l.{
-  (if (isfull l)
-    ((if (peek l) 1 0) (self (pop l)))
-    END
-  )
-})
-
-one := (push T nil)
-double N := (push F N)
-
-N :=
-  (double (double (double (double (double
-  (double (double (double (double (double
-  (double (double (double (double (double
-  (double (double (double (double (double
-  (double (double (double (double (double
-  (double (double (double (double (double
-  one))))))))))))))))))))))))))))))
-
-(print N)

samples/simple.txt

@@ -1,16 +0,0 @@
-(\0.
-  (\inc.
-    (\add.
-      (\mult.
-        (\exp.
-          (exp (inc (inc (inc (inc 0)))) (inc (inc (inc (inc (inc 0))))))
-          \n m.(m n)
-        )
-        \m n f.(m (n f))
-      )
-      \n m.(m inc n)
-    )
-    \n f x.(f (n f x))
-  )
-  \f x.x
-)

samples/thunk.txt

@@ -1 +0,0 @@
-(\.VALUE anything)