From ec6172f07edf81d8e8be22b2b4b4d7190316ce95 Mon Sep 17 00:00:00 2001
From: Helmut Merz <helmutm@cy55.de>
Date: Thu, 20 Jul 2023 19:51:43 +0200
Subject: [PATCH] work in progress: add some 'Forge' (Forth by Go)
 functionality

---
 forge/forge.go       |  2 ++
 forge/stack/stack.go | 53 ++++++++++++++++++++++++++++++++++++++++++++
 forge/voc/voc.go     | 42 +++++++++++++++++++++++++++++++++++
 tests/forge_test.go  | 44 ++++++++++++++++++++++++++++++++++++
 4 files changed, 141 insertions(+)
 create mode 100644 forge/forge.go
 create mode 100644 forge/stack/stack.go
 create mode 100644 forge/voc/voc.go
 create mode 100644 tests/forge_test.go

diff --git a/forge/forge.go b/forge/forge.go
new file mode 100644
index 0000000..59e8311
--- /dev/null
+++ b/forge/forge.go
@@ -0,0 +1,2 @@
+// Package forge implements sort of a stack-based interpreter.
+package forge
diff --git a/forge/stack/stack.go b/forge/stack/stack.go
new file mode 100644
index 0000000..c326c9b
--- /dev/null
+++ b/forge/stack/stack.go
@@ -0,0 +1,53 @@
+// package stack provides a generic first-in / first-out stack.
+package stack
+
+// stack interface
+
+type Stack[V any] interface {
+	Depth() int
+	Push(V)
+	Pop() V
+	Peek(int) V
+	Replace(int, V)
+}
+
+// simple slice implementation
+
+type stack[V any] struct {
+	tos  int
+	data []V
+}
+
+func NewStack[V any]() *stack[V] {
+	return &stack[V]{
+		tos:  -1,
+		data: make([]V, 0, 5),
+	}
+}
+
+func (st *stack[V]) Depth() int {
+	return st.tos + 1
+}
+
+func (st *stack[V]) Push(v V) {
+	st.tos += 1
+	if st.tos >= len(st.data) {
+		st.data = append(st.data, v)
+	} else {
+		st.data[st.tos] = v
+	}
+}
+
+func (st *stack[V]) Pop() V {
+	v := st.data[st.tos]
+	st.tos -= 1
+	return v
+}
+
+func (st *stack[V]) Peek(i int) V {
+	return st.data[st.tos-i]
+}
+
+func (st *stack[V]) Replace(i int, v V) {
+	st.data[st.tos-i] = v
+}
diff --git a/forge/voc/voc.go b/forge/voc/voc.go
new file mode 100644
index 0000000..29a4c9d
--- /dev/null
+++ b/forge/voc/voc.go
@@ -0,0 +1,42 @@
+// Package voc implements a generic vocabulary. Vocabularies may be nested
+// and are searched upwards using the parent vocabulary until this is nil.
+// Individual entries contain slices of values; the last item in a
+// slice is the current value.
+package voc
+
+import (
+	"git.sr.ht/~cco/go-scopes/lib/funky"
+)
+
+type VocData[V any] map[string][]V
+
+type Vocabulary[V any] struct {
+	parent *Vocabulary[V]
+	data   VocData[V]
+}
+
+func NewVoc[V any](parent *Vocabulary[V]) *Vocabulary[V] {
+	return &Vocabulary[V]{
+		parent: parent,
+		data:   VocData[V]{},
+	}
+}
+func (voc *Vocabulary[V]) Register(name string, it V) {
+	vi, ok := voc.data[name]
+	if ok {
+		voc.data[name] = append(vi, it)
+	} else {
+		voc.data[name] = []V{it}
+	}
+}
+
+func (voc *Vocabulary[V]) Lookup(name string) funky.Maybe[V] {
+	vi, ok := voc.data[name]
+	if ok {
+		return funky.Just(vi[len(vi)-1])
+	}
+	if voc.parent != nil {
+		return voc.parent.Lookup(name)
+	}
+	return funky.Nothing[V]()
+}
diff --git a/tests/forge_test.go b/tests/forge_test.go
new file mode 100644
index 0000000..315fb76
--- /dev/null
+++ b/tests/forge_test.go
@@ -0,0 +1,44 @@
+package scopes_test
+
+import (
+	tbase "testing"
+
+	"git.sr.ht/~cco/go-scopes/forge/stack"
+	"git.sr.ht/~cco/go-scopes/forge/voc"
+	"git.sr.ht/~cco/go-scopes/testing"
+)
+
+func TestForge(tb *tbase.T) {
+	t := testing.SetUp(tb)
+	t.Run("stack", StackTest)
+	t.Run("voc", VocTest)
+}
+
+func StackTest(t *testing.T) {
+	var st stack.Stack[int] = stack.NewStack[int]()
+	st.Push(3)
+	st.Push(4)
+	t.AssertEqual(st.Depth(), 2)
+	st.Push(5)
+	t.AssertEqual(st.Peek(0), 5)
+	st.Replace(1, 99)
+	st.Push(6)
+	t.AssertEqual(st.Peek(2), 99)
+	st.Push(7)
+	st.Push(8)
+	st.Push(9)
+	t.AssertEqual(st.Peek(2), 7)
+	st.Pop()
+	t.AssertEqual(st.Pop(), 8)
+	t.AssertEqual(st.Peek(st.Depth()-1), 3)
+}
+
+func VocTest(t *testing.T) {
+	v1 := voc.NewVoc[int](nil)
+	v1.Register("one", 1)
+	m := v1.Lookup("one")
+	t.AssertEqual(m.IsNothing(), false)
+	t.AssertEqual(m.Value(), 1)
+	m = v1.Lookup("two")
+	t.AssertEqual(m.IsNothing(), true)
+}