Added map-lines and upgraded UCL

plugins.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -18,7 +20,6 @@ const pluginKeyPrefix = "plugin:"
 
 // PluginFilters is the registry of text filters defined by UCL plugin files.
 type PluginFilters struct {
-	inst    *ucl.Inst
 	filters map[string]TextProcessor
 	errors  []error
 }
@@ -34,7 +35,8 @@ func (p *PluginFilters) Module() ucl.Module {
 	return ucl.Module{
 		Name: "d",
 		Builtins: map[string]ucl.BuiltinHandler{
-			"filter": p.filterBuiltin,
+			"filter":    p.filterBuiltin,
+			"map-lines": p.mapLinesBuiltin,
 		},
 	}
 }
@@ -78,6 +80,51 @@ func (p *PluginFilters) filterBuiltin(ctx context.Context, args ucl.CallArgs) (a
 	return nil, nil
 }
 
+// mapLinesBuiltin implements `d:map-lines INPUT PROC` which applies a transform for each line of the input.
+func (p *PluginFilters) mapLinesBuiltin(ctx context.Context, args ucl.CallArgs) (any, error) {
+	var (
+		input string
+		proc  ucl.Invokable
+	)
+
+	if err := args.Bind(&input, &proc); err != nil {
+		return nil, fmt.Errorf("d:map-lines: expected INPUT and PROC: %w", err)
+	}
+
+	var (
+		dst     bytes.Buffer
+		dstLine bytes.Buffer
+	)
+
+	scnr := bufio.NewScanner(strings.NewReader(input))
+	isFirst := true
+	for scnr.Scan() {
+		dstLine.Reset()
+		line := scnr.Text()
+
+		out, err := proc.Invoke(ctx, line)
+		if err != nil {
+			return TextFilterResponse{}, err
+		} else if out == nil {
+			continue
+		} else if strOut, ok := out.(fmt.Stringer); ok {
+			dstLine.WriteString(strOut.String())
+		} else {
+			dstLine.WriteString(fmt.Sprint(out))
+		}
+
+		if isFirst {
+			isFirst = false
+		} else {
+			dst.WriteString("\n")
+		}
+
+		dst.WriteString(dstLine.String())
+	}
+
+	return dst.String(), nil
+}
+
 // LoadDir evaluates every *.ucl file found under dir (recursively, in lexical order). Files
 // that fail to load are recorded in Errors() and skipped; loading continues with the rest.
 // A missing directory is not an error.