From 62d5eed79db59f6685f775b12c6d480e20a43aac Mon Sep 17 00:00:00 2001
From: sloum <sloum@colorfield.space>
Date: Thu, 4 May 2023 14:21:07 -0700
Subject: [PATCH] Adds simple typing implementation

---
 gui.go         | 21 ++++++++++++++++++++-
 interpreter.go | 37 ++++++++++++++++++++++++++++++++++++-
 nogui.go       | 21 ++++++++++++++++++++-
 3 files changed, 76 insertions(+), 3 deletions(-)

diff --git a/gui.go b/gui.go
index 1a48daa..182a272 100644
--- a/gui.go
+++ b/gui.go
@@ -1130,7 +1130,26 @@ func String(v expression, rawString bool) string {
 	case proc:
 		var b strings.Builder
 		b.WriteString("(lambda ")
-		b.WriteString(String(v.params, true))
+		params, ok := v.params.([]expression)
+		if len(v.predicates) > 0 {
+			if ok {
+				newParams := make([]expression, len(params))
+				copy(newParams, params)
+				for i := range newParams {
+					if pred, ok := v.predicates[newParams[i].(symbol)]; ok {
+						newParams[i] = symbol(fmt.Sprintf("%s@%s", newParams[i].(symbol), pred))
+					}
+				}
+				b.WriteString(String(newParams, true))
+			} else {
+				val := String(v.params, false)
+				b.WriteString(val)
+				b.WriteString("@")
+				b.WriteString(string(v.predicates[symbol(val)]))
+			}
+		} else {
+			b.WriteString(String(v.params, true))
+		}
 		b.WriteRune(' ')
 		body := String(v.body, true)
 		if strings.HasPrefix(body, "(begin ") {
diff --git a/interpreter.go b/interpreter.go
index 3818e0b..000fdc2 100644
--- a/interpreter.go
+++ b/interpreter.go
@@ -17,6 +17,7 @@ type proc struct {
 	params expression
 	body   expression
 	en     *env
+	predicates map[symbol]symbol
 }
 
 type macro struct {
@@ -280,7 +281,31 @@ func eval(exp expression, en *env) (value expression) {
 			}
 			b := []expression{symbol("begin")}
 			b = append(b, e[2:]...)
-			value = proc{e[1], stringUnescapeEval(b), en}
+			predicates := make(map[symbol]symbol)
+			switch a := e[1].(type) {
+			case []expression:
+				for i, v := range a {
+					s := String(v, false)
+					ind := strings.LastIndex(s, "@")
+					if ind < 1 {
+						continue
+					}
+					a[i] = symbol(s[:ind])
+					predicates[a[i].(symbol)] = symbol(s[ind+1:])
+				}
+				e[1] = a
+			default:
+				s := String(e[1], false)
+				ind := strings.LastIndex(s, "@")
+				if ind < 1 {
+					e[1] = []expression{e[1]}
+					break
+				}
+				e[1] = symbol(s[:ind])
+				predicates[e[1].(symbol)] = symbol(s[ind+1:])
+				e[1] = []expression{e[1]}
+			}
+			value = proc{e[1], stringUnescapeEval(b), en, predicates}
 		case "macro":
 			if len(e) < 3 {
 				value = exception("'macro' expects at least three arguments")
@@ -716,9 +741,19 @@ func apply(procedure expression, args []expression, name expression) (value expr
 					}
 					break
 				}
+				if v, ok := p.predicates[param.(symbol)]; ok {
+					if !AnythingToBool(eval([]expression{v, args[i]}, p.en)).(bool) {
+						return exception(fmt.Sprintf("Type Error: Lambda %q expected argument %d to pass predicate %q, it did not", String(name, false), i+1, v))
+					}
+				}
 				en.vars[param.(symbol)] = args[i]
 			}
 		default:
+			if v, ok := p.predicates[params.(symbol)]; ok {
+				if !AnythingToBool(eval([]expression{v, args[0]}, p.en)).(bool) {
+					return exception(fmt.Sprintf("Type Error: Lambda %q expected argument %d to pass predicate %q, it did not", String(name, false), 1, v))
+				}
+			}
 			en.vars[params.(symbol)] = args
 		}
 		value = eval(p.body, en)
diff --git a/nogui.go b/nogui.go
index b3a0287..ee6e688 100644
--- a/nogui.go
+++ b/nogui.go
@@ -35,7 +35,26 @@ func String(v expression, rawString bool) string {
 	case proc:
 		var b strings.Builder
 		b.WriteString("(lambda ")
-		b.WriteString(String(v.params, true))
+		params, ok := v.params.([]expression)
+		if len(v.predicates) > 0 {
+			if ok {
+				newParams := make([]expression, len(params))
+				copy(newParams, params)
+				for i := range newParams {
+					if pred, ok := v.predicates[newParams[i].(symbol)]; ok {
+						newParams[i] = symbol(fmt.Sprintf("%s@%s", newParams[i].(symbol), pred))
+					}
+				}
+				b.WriteString(String(newParams, true))
+			} else {
+				val := String(v.params, false)
+				b.WriteString(val)
+				b.WriteString("@")
+				b.WriteString(string(v.predicates[symbol(val)]))
+			}
+		} else {
+			b.WriteString(String(v.params, true))
+		}
 		b.WriteRune(' ')
 		body := String(v.body, true)
 		if strings.HasPrefix(body, "(begin ") {