func-bolerplate.bash: generate Go source for a new functions module

Also fixed mul() function that called doAdd() instead of doMul().

common-errors.go

@@ -0,0 +1,37 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// common-errors.go
+package expr
+
+import (
+	"fmt"
+)
+
+// --- General errors
+
+func errCantConvert(funcName string, value any, kind string) error {
+	return fmt.Errorf("%s() can't convert %T to %s", funcName, value, kind)
+}
+
+func errExpectedGot(funcName string, kind string, value any) error {
+	return fmt.Errorf("%s() expected %s, got %T (%v)", funcName, kind, value, value)
+}
+
+// --- Parameter errors
+
+func errOneParam(funcName string) error {
+	return fmt.Errorf("%s() requires exactly one param", funcName)
+}
+
+func errMissingRequiredParameter(funcName, paramName string) error {
+	return fmt.Errorf("%s() missing required parameter %q", funcName, paramName)
+}
+
+func errInvalidParameterValue(funcName, paramName string, paramValue any) error {
+	return fmt.Errorf("%s() invalid value %T (%v) for parameter %q", funcName, paramValue, paramValue, paramName)
+}
+
+func errWrongParamType(funcName, paramName, paramType string, paramValue any) error {
+	return fmt.Errorf("%s() the %q parameter must be a %s, got a %T (%v)", funcName, paramName, paramType, paramValue, paramValue)
+}

common-params.go

@@ -0,0 +1,11 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// common-params.go
+package expr
+
+const (
+	paramParts     = "parts"
+	paramSeparator = "separator"
+	paramSource    = "source"
+)

common-type-names.go

@@ -0,0 +1,13 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// common-type-names.go
+package expr
+
+const (
+	typeBoolean = "boolean"
+	typeFloat   = "decimal"
+	typeInt     = "integer"
+	typeNumber  = "number"
+	typeString  = "string"
+)

context-helpers.go

@@ -27,8 +27,10 @@ func exportFunc(ctx ExprContext, name string, info ExprFunc) {
 
 func exportObjects(destCtx, sourceCtx ExprContext) {
 	exportAll := isEnabled(sourceCtx, control_export_all)
+	// fmt.Printf("Exporting from sourceCtx [%p] to destCtx [%p] -- exportAll=%t\n", sourceCtx, destCtx, exportAll)
 	// Export variables
 	for _, refName := range sourceCtx.EnumVars(func(name string) bool { return exportAll || name[0] == '@' }) {
+		// fmt.Printf("\tExporting %q\n", refName)
 		refValue, _ := sourceCtx.GetVar(refName)
 		exportVar(destCtx, refName, refValue)
 	}

data-cursor.go

@@ -6,7 +6,9 @@ package expr
 
 import (
 	"errors"
+	"fmt"
 	"io"
+	"strings"
 )
 
 const (
@@ -18,7 +20,7 @@ const (
 )
 
 type dataCursor struct {
-	ds          map[any]*term
+	ds          map[string]Functor
 	ctx         ExprContext
 	index       int
 	resource    any
@@ -28,36 +30,93 @@ type dataCursor struct {
 	currentFunc Functor
 }
 
-func newDataCursor(ctx ExprContext) (dc *dataCursor) {
+func newDataCursor(ctx ExprContext, ds map[string]Functor) (dc *dataCursor) {
 	dc = &dataCursor{
+		ds:    ds,
 		index: -1,
 		ctx:   ctx.Clone(),
 	}
 	return
 }
 
+func mapToString(m map[string]Functor) string {
+	var sb strings.Builder
+	sb.WriteByte('{')
+	for key, _ := range m {
+		if sb.Len() > 1 {
+			sb.WriteString(fmt.Sprintf(", %q: func(){}", key))
+		} else {
+			sb.WriteString(fmt.Sprintf("%q: func(){}", key))
+		}
+	}
+	sb.WriteByte('}')
+	return sb.String()
+}
+
 func (dc *dataCursor) String() string {
-	return "$(...)"
+	return "$()"
+/*	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf(`$(
+	index: %d,
+	ds:    %s,
+	ctx:   `, dc.index, mapToString(dc.ds)))
+	CtxToBuilder(&sb, dc.ctx, 1)
+	sb.WriteByte(')')
+	return sb.String()
+*/
+}
+
+func (dc *dataCursor) HasOperation(name string) (exists bool) {
+	f, ok := dc.ds[name]
+	exists = ok && isFunctor(f)
+	return
+}
+
+func (dc *dataCursor) CallOperation(name string, args []any) (value any, err error) {
+	if functor, ok := dc.ds[name]; ok && isFunctor(functor) {
+		if functor == dc.cleanFunc {
+			return nil, dc.Clean()
+		} else if functor == dc.resetFunc {
+			return nil, dc.Reset()
+		} else {
+			ctx := cloneContext(dc.ctx)
+			value, err = functor.Invoke(ctx, name, []any{})
+			exportObjects(dc.ctx, ctx)
+		}
+
+	} else {
+		err = errNoOperation(name)
+	}
+	return
 }
 
 func (dc *dataCursor) Reset() (err error) {
 	if dc.resetFunc != nil {
-		ctx := cloneContext(dc.ctx)
-		if _, err = dc.resetFunc.Invoke(ctx, resetName, []any{}); err == nil {
-			dc.index = -1
+		if dc.resource != nil {
+			ctx := cloneContext(dc.ctx)
+			if _, err = dc.resetFunc.Invoke(ctx, resetName, []any{dc.resource}); err == nil {
+				dc.index = -1
+			}
+			exportObjects(dc.ctx, ctx)
+		} else {
+			err = errInvalidDataSource()
 		}
-		exportObjects(dc.ctx, ctx)
 	} else {
-		err = errors.New("no 'reset' function defined in the data-source")
+		err = errNoOperation(resetName)
 	}
 	return
 }
 
 func (dc *dataCursor) Clean() (err error) {
 	if dc.cleanFunc != nil {
-		ctx := cloneContext(dc.ctx)
-		_, err = dc.cleanFunc.Invoke(ctx, cleanName, []any{})
-		exportObjects(dc.ctx, ctx)
+		if dc.resource != nil {
+			ctx := cloneContext(dc.ctx)
+			_, err = dc.cleanFunc.Invoke(ctx, cleanName, []any{dc.resource})
+			dc.resource = nil
+			exportObjects(dc.ctx, ctx)
+		} else {
+			err = errInvalidDataSource()
+		}
 	} else {
 		err = errors.New("no 'clean' function defined in the data-source")
 	}
@@ -74,15 +133,22 @@ func (dc *dataCursor) Current() (item any, err error) { // must return io.EOF at
 }
 
 func (dc *dataCursor) Next() (item any, err error) { // must return io.EOF after the last item
-	ctx := cloneContext(dc.ctx)
-	if item, err = dc.nextFunc.Invoke(ctx, nextName, []any{}); err == nil {
-		if item == nil {
-			err = io.EOF
-		} else {
-			dc.index++
+	if dc.resource != nil {
+		ctx := cloneContext(dc.ctx)
+		// fmt.Printf("Entering Inner-Ctx [%p]: %s\n", ctx, CtxToString(ctx, 0))
+		if item, err = dc.nextFunc.Invoke(ctx, nextName, []any{dc.resource}); err == nil {
+			if item == nil {
+				err = io.EOF
+			} else {
+				dc.index++
+			}
 		}
+		// fmt.Printf("Exiting Inner-Ctx [%p]: %s\n", ctx, CtxToString(ctx, 0))
+		exportObjects(dc.ctx, ctx)
+		// fmt.Printf("Outer-Ctx [%p]: %s\n", dc.ctx, CtxToString(dc.ctx, 0))
+	} else {
+		err = errInvalidDataSource()
 	}
-	exportObjects(dc.ctx, ctx)
 	return
 }
 

func-common.go

@@ -1,17 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// func-common.go
-package expr
-
-import (
-	"fmt"
-)
-
-func errOneParam(funcName string) error {
-	return fmt.Errorf("%s() requires exactly one param", funcName)
-}
-
-func errCantConvert(funcName string, value any, kind string) error {
-	return fmt.Errorf("%s() can't convert %T to %s", funcName, value, kind)
-}

func-math.go

@@ -10,7 +10,7 @@ import (
 )
 
 func checkNumberParamExpected(funcName string, paramValue any, paramPos int) (err error) {
-	if !(isNumber(paramValue) || isList(paramValue)) {
+	if !(isNumber(paramValue) || isList(paramValue) || isIterator(paramValue)) {
 		err = fmt.Errorf("%s(): param nr %d has wrong type %T, number expected", funcName, paramPos+1, paramValue)
 	}
 	return
@@ -27,6 +27,11 @@ func doAdd(ctx ExprContext, name string, it Iterator) (result any, err error) {
 			if v, err = doAdd(ctx, name, subIter); err != nil {
 				break
 			}
+			if subIter.HasOperation(cleanName) {
+				if _, err = subIter.CallOperation(cleanName, nil); err != nil {
+					return
+				}
+			}
 		} else {
 			if err = checkNumberParamExpected(name, v, it.Index()); err != nil {
 				break
@@ -77,7 +82,7 @@ func doMul(ctx ExprContext, name string, it Iterator) (result any, err error) {
 		}
 
 		if array, ok := v.([]any); ok {
-			if v, err = doAdd(ctx, name, NewFlatArrayIterator(array)); err != nil {
+			if v, err = doMul(ctx, name, NewFlatArrayIterator(array)); err != nil {
 				break
 			}
 		}

func-os.go

@@ -126,7 +126,7 @@ func writeFileFunc(ctx ExprContext, name string, args []any) (result any, err er
 
 func readFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	var handle osHandle
-
+	result = nil
 	if len(args) > 0 {
 		handle, _ = args[0].(osHandle)
 	}
@@ -141,13 +141,16 @@ func readFileFunc(ctx ExprContext, name string, args []any) (result any, err err
 						limit = s[0]
 					}
 				}
-				if v, err = r.reader.ReadString(limit); err == nil || err == io.EOF {
+				if v, err = r.reader.ReadString(limit); err == nil {
 					if len(v) > 0 && v[len(v)-1] == limit {
 						result = v[0 : len(v)-1]
 					} else {
 						result = v
 					}
 				}
+				if err == io.EOF {
+					err = nil
+				}
 			}
 		}
 	}

func-string.go

@@ -0,0 +1,118 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// func-string.go
+package expr
+
+import (
+	"io"
+	"strings"
+)
+
+// --- Start of function definitions
+func doJoinStr(funcName string, sep string, it Iterator) (result any, err error) {
+	var sb strings.Builder
+	var v any
+	for v, err = it.Next(); err == nil; v, err = it.Next() {
+		if it.Index() > 0 {
+			sb.WriteString(sep)
+		}
+		if s, ok := v.(string); ok {
+			sb.WriteString(s)
+		} else {
+			err = errExpectedGot(funcName, typeString, v)
+			return
+		}
+	}
+	if err == nil || err == io.EOF {
+		err = nil
+		result = sb.String()
+	}
+	return
+}
+
+func joinStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	if len(args) < 1 {
+		return nil, errMissingRequiredParameter(name, paramSeparator)
+	}
+	if sep, ok := args[0].(string); ok {
+		if len(args) == 1 {
+			result = ""
+		} else if len(args) == 2 {
+			if ls, ok := args[1].([]any); ok {
+				result, err = doJoinStr(name, sep, NewFlatArrayIterator(ls))
+			} else if it, ok := args[1].(Iterator); ok {
+				result, err = doJoinStr(name, sep, it)
+			} else {
+				err = errInvalidParameterValue(name, paramParts, args[1])
+			}
+		} else {
+			result, err = doJoinStr(name, sep, NewFlatArrayIterator(args[1:]))
+		}
+	} else {
+		err = errWrongParamType(name, paramSeparator, typeString, args[0])
+	}
+	return
+}
+
+func subStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var start = 0
+	var count = -1
+	var source string
+	var ok bool
+
+	if len(args) < 1 {
+		return nil, errMissingRequiredParameter(name, paramSource)
+	}
+	if source, ok = args[0].(string); !ok {
+		return nil, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	if len(args) > 1 {
+		if start, err = toInt(args[1], name+"()"); err != nil {
+			return
+		}
+		if len(args) > 2 {
+			if count, err = toInt(args[2], name+"()"); err != nil {
+				return
+			}
+		}
+		if start < 0 {
+			start = len(source) + start
+		}
+	}
+	if count < 0 {
+		count = len(source) - start
+	}
+	end := min(start+count, len(source))
+	result = source[start:end]
+	return
+}
+
+func trimStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var source string
+	var ok bool
+
+	if len(args) < 1 {
+		return nil, errMissingRequiredParameter(name, paramSource)
+	}
+	if source, ok = args[0].(string); !ok {
+		return nil, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	result = strings.TrimSpace(source)
+	return
+}
+
+// --- End of function definitions
+
+// Import above functions in the context
+func ImportStringFuncs(ctx ExprContext) {
+	ctx.RegisterFunc("joinStr", &simpleFunctor{f: joinStrFunc}, 1, -1)
+	ctx.RegisterFunc("subStr", &simpleFunctor{f: subStrFunc}, 1, -1)
+	ctx.RegisterFunc("trimStr", &simpleFunctor{f: trimStrFunc}, 1, -1)
+}
+
+// Register the import function in the import-register.
+// That will allow to import all function of this module by the "builtin" operator."
+func init() {
+	registerImport("string", ImportStringFuncs, "string utilities")
+}

iter-list.go

@@ -15,6 +15,14 @@ func NewFlatArrayIterator(array []any) *FlatArrayIterator {
 	return &FlatArrayIterator{a: array, index: 0}
 }
 
+func (it *FlatArrayIterator) HasOperation(name string) bool {
+	return false
+}
+
+func (it *FlatArrayIterator) CallOperation(name string, args []any) (any, error) {
+	return nil, errNoOperation(name)
+}
+
 func (it *FlatArrayIterator) Current() (item any, err error) {
 	if it.index >= 0 && it.index < len(it.a) {
 		item = it.a[it.index]

iterator.go

@@ -4,8 +4,23 @@
 // iterator.go
 package expr
 
+import (
+	"errors"
+	"fmt"
+)
+
 type Iterator interface {
 	Next() (item any, err error) // must return io.EOF after the last item
 	Current() (item any, err error)
 	Index() int
+	HasOperation(name string) bool
+	CallOperation(name string, args []any) (value any, err error)
+}
+
+func errNoOperation(name string) error {
+	return fmt.Errorf("no %q function defined in the data-source", name)
+}
+
+func errInvalidDataSource() error {
+	return errors.New("invalid data-source")
 }

operand-func.go

@@ -24,6 +24,7 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
 	ctx := cloneContext(parentCtx)
 	name, _ := self.tk.Value.(string)
+	// fmt.Printf("Call %s(), context: %p\n", name, ctx)
 	params := make([]any, len(self.children))
 	for i, tree := range self.children {
 		var param any

operand-iterator.go

@@ -6,6 +6,8 @@ package expr
 
 import (
 	"fmt"
+	"slices"
+	"strings"
 )
 
 // -------- iterator term
@@ -41,6 +43,44 @@ func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
 	return
 }
 
+// func getDataSourceDict(ctx ExprContext, self *term) (ds map[string]Functor, err error) {
+// 	var value any
+// 	if len(self.children) < 1 || self.children[0] == nil {
+// 		err = self.Errorf("missing the data-source parameter")
+// 		return
+// 	}
+
+// 	if value, err = self.children[0].compute(ctx); err != nil {
+// 		return
+// 	}
+
+// 	if dictAny, ok := value.(map[any]any); ok {
+// 		ds = make(map[string]Functor)
+// 		// required functions
+// 		for _, k := range []string{currentName, nextName} {
+// 			if item, exists := dictAny[k]; exists && item != nil {
+// 				if functor, ok := item.(*funcDefFunctor); ok {
+// 					ds[k] = functor
+// 				}
+// 			} else {
+// 				err = fmt.Errorf("the data-source must provide a non-nil %q operator", k)
+// 				return
+// 			}
+// 		}
+// 		// Optional functions
+// 		for _, k := range []string{initName, resetName, cleanName} {
+// 			if item, exists := dictAny[k]; exists && item != nil {
+// 				if functor, ok := item.(*funcDefFunctor); ok {
+// 					ds[k] = functor
+// 				}
+// 			}
+// 		}
+// 	} else {
+// 		err = self.Errorf("the first param (data-source) of an iterator must be a dict, not a %T", value)
+// 	}
+// 	return
+// }
+
 func getDataSourceDict(ctx ExprContext, self *term) (ds map[string]Functor, err error) {
 	var value any
 	if len(self.children) < 1 || self.children[0] == nil {
@@ -52,26 +92,30 @@ func getDataSourceDict(ctx ExprContext, self *term) (ds map[string]Functor, err
 		return
 	}
 
+	requiredFields := []string{currentName, nextName}
+	fieldsMask := 0b11
+	foundFields := 0
 	if dictAny, ok := value.(map[any]any); ok {
 		ds = make(map[string]Functor)
-		// required functions
-		for _, k := range []string{currentName, nextName} {
-			if item, exists := dictAny[k]; exists && item != nil {
+		for keyAny, item := range dictAny {
+			if key, ok := keyAny.(string); ok {
 				if functor, ok := item.(*funcDefFunctor); ok {
-					ds[k] = functor
+					ds[key] = functor
+					if index := slices.Index(requiredFields, key); index >= 0 {
+						foundFields |= 1 << index
+					}
 				}
-			} else {
-				err = fmt.Errorf("the data-source must provide a non-nil %q operator", k)
-				return
 			}
 		}
-		// Optional functions
-		for _, k := range []string{initName, resetName, cleanName} {
-			if item, exists := dictAny[k]; exists && item != nil {
-				if functor, ok := item.(*funcDefFunctor); ok {
-					ds[k] = functor
+		// check required functions
+		if foundFields != fieldsMask {
+			missingFields := make([]string, 0, len(requiredFields))
+			for index, field := range requiredFields {
+				if (foundFields & (1 << index)) == 0 {
+					missingFields = append(missingFields, field)
 				}
 			}
+			err = fmt.Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
 		}
 	} else {
 		err = self.Errorf("the first param (data-source) of an iterator must be a dict, not a %T", value)
@@ -86,8 +130,9 @@ func evalIterator(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	dc := newDataCursor(ctx)
-
+	dc := newDataCursor(ctx, ds)
+	// var it Iterator = dc
+	// fmt.Println(it)
 	if initFunc, exists := ds[initName]; exists && initFunc != nil {
 		var args []any
 		if len(self.children) > 1 {

simple-func-store.go

@@ -44,9 +44,11 @@ func NewSimpleFuncStore() *SimpleFuncStore {
 }
 
 func (ctx *SimpleFuncStore) Clone() ExprContext {
+	svs := ctx.SimpleVarStore
 	return &SimpleFuncStore{
-		SimpleVarStore: SimpleVarStore{varStore: CloneMap(ctx.varStore)},
-		funcStore:      CloneMap(ctx.funcStore),
+		// SimpleVarStore: SimpleVarStore{varStore: CloneMap(ctx.varStore)},
+		SimpleVarStore: SimpleVarStore{varStore: svs.cloneVars()},
+		funcStore:      CloneFilteredMap(ctx.funcStore, func(name string) bool { return name[0] != '@' }),
 	}
 }
 

simple-var-store.go

@@ -4,7 +4,10 @@
 // simple-var-store.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 type SimpleVarStore struct {
 	varStore map[string]any
@@ -16,9 +19,14 @@ func NewSimpleVarStore() *SimpleVarStore {
 	}
 }
 
+func (ctx *SimpleVarStore) cloneVars() (vars map[string]any) {
+	return CloneFilteredMap(ctx.varStore, func(name string) bool { return name[0] != '@' })
+}
+
 func (ctx *SimpleVarStore) Clone() (clone ExprContext) {
+	// fmt.Println("*** Cloning context ***")
 	clone = &SimpleVarStore{
-		varStore: CloneMap(ctx.varStore),
+		varStore: ctx.cloneVars(),
 	}
 	return clone
 }
@@ -29,10 +37,12 @@ func (ctx *SimpleVarStore) GetVar(varName string) (v any, exists bool) {
 }
 
 func (ctx *SimpleVarStore) setVar(varName string, value any) {
+	// fmt.Printf("[%p] setVar(%v, %v)\n", ctx, varName, value)
 	ctx.varStore[varName] = value
 }
 
 func (ctx *SimpleVarStore) SetVar(varName string, value any) {
+	// fmt.Printf("[%p] SetVar(%v, %v)\n", ctx, varName, value)
 	if allowedValue, ok := fromGenericAny(value); ok {
 		ctx.varStore[varName] = allowedValue
 	} else {
@@ -68,3 +78,35 @@ func (ctx *SimpleVarStore) RegisterFunc(name string, functor Functor, minArgs, m
 func (ctx *SimpleVarStore) EnumFuncs(acceptor func(name string) (accept bool)) (funcNames []string) {
 	return
 }
+
+func CtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
+	sb.WriteString("{\n")
+	first := true
+	for _, name := range ctx.EnumVars(func(name string) bool { return name[0] != '_' }) {
+		value, _ := ctx.GetVar(name)
+		sb.WriteString(strings.Repeat("\t", indent+1))
+		sb.WriteString(name)
+		sb.WriteString("=")
+		if _, ok := value.(Functor); ok {
+			sb.WriteString(": func(){}")
+		} else if _, ok = value.(map[any]any); ok {
+			sb.WriteString("dict{}")
+		} else {
+			sb.WriteString(fmt.Sprintf("%v", value))
+		}
+		if first {
+			first = false
+		} else {
+			sb.WriteByte(',')
+		}
+		sb.WriteByte('\n')
+	}
+	sb.WriteString(strings.Repeat("\t", indent))
+	sb.WriteString("}\n")
+}
+
+func CtxToString(ctx ExprContext, indent int) string {
+	var sb strings.Builder
+	CtxToBuilder(&sb, ctx, indent)
+	return sb.String()
+}

term.go

@@ -154,7 +154,7 @@ func (self *term) toInt(computedValue any, valueDescription string) (i int, err
 	if index64, ok := computedValue.(int64); ok {
 		i = int(index64)
 	} else {
-		err = self.Errorf("%s, got %T", valueDescription, computedValue)
+		err = self.Errorf("%s, got %T (%v)", valueDescription, computedValue, computedValue)
 	}
 	return
 }

tools/func-bolerplate.bash

@@ -0,0 +1,71 @@
+#!/usr/bin/env bash
+
+if [ $# -lt 2 ]; then
+	echo >&2 "Usage: $(basename "${0}") <module-name> <func-name>..."
+	exit 1
+fi
+
+MODULE_NAME=${1,,}
+GO_FILE="func-${MODULE_NAME//[-.]/_}.go"
+
+shift
+FUNC_LIST=
+i=0
+for name; do
+	if [ ${i} -gt 0 ]; then
+		if [ $((i+1)) -eq $# ]; then
+			FUNC_LIST+=" and "
+		else
+			FUNC_LIST+=", "
+		fi
+	fi
+	FUNC_LIST+="${name}()"
+	((i++))
+done
+
+cat > "${GO_FILE}" <<EOF
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// func-${MODULE_NAME}.go
+package expr
+
+import (
+)
+
+
+// --- Start of function definitions
+
+$(
+for name; do
+	cat <<IEOF
+func ${name}Func(ctx ExprContext, name string, args []any) (result any, err error) {
+        return
+}
+
+IEOF
+
+done
+)
+
+// --- End of function definitions
+
+// Import above functions in the context
+func Import${MODULE_NAME^}Funcs(ctx ExprContext) {
+$(
+for name; do
+        cat <<IEOF
+        ctx.RegisterFunc("${name}", &simpleFunctor{f: ${name}Func}, 1, -1)
+IEOF
+
+done
+)
+}
+
+// Register the import function in the import-register.
+// That will allow to import all function of this module by the "builtin" operator."
+func init() {
+	registerImport("${MODULE_NAME}", Import${name}Funcs, "The \"${MODULE_NAME}\" module implements the ${FUNC_LIST} function(s)")
+}
+EOF
+

utils.go

@@ -4,7 +4,10 @@
 // utils.go
 package expr
 
-import "reflect"
+import (
+	"fmt"
+	"reflect"
+)
 
 func isString(v any) (ok bool) {
 	_, ok = v.(string)
@@ -39,6 +42,16 @@ func isNumberString(v any) (ok bool) {
 	return isString(v) || isNumber(v)
 }
 
+func isFunctor(v any) (ok bool) {
+	_, ok = v.(Functor)
+	return
+}
+
+func isIterator(v any) (ok bool) {
+	_, ok = v.(Iterator)
+	return
+}
+
 func numAsFloat(v any) (f float64) {
 	var ok bool
 	if f, ok = v.(float64); !ok {
@@ -136,3 +149,32 @@ func CloneMap[K comparable, V any](source map[K]V) map[K]V {
 	dest := make(map[K]V, len(source))
 	return CopyMap(dest, source)
 }
+
+func CopyFilteredMap[K comparable, V any](dest, source map[K]V, filter func(key K) (accept bool)) map[K]V {
+	// fmt.Printf("--- Clone with filter %p\n", filter)
+	if filter == nil {
+		return CopyMap(dest, source)
+	} else {
+		for k, v := range source {
+			if filter(k) {
+				// fmt.Printf("\tClone var %q\n", k)
+				dest[k] = v
+			}
+		}
+	}
+	return dest
+}
+
+func CloneFilteredMap[K comparable, V any](source map[K]V, filter func(key K) (accept bool)) map[K]V {
+	dest := make(map[K]V, len(source))
+	return CopyFilteredMap(dest, source, filter)
+}
+
+func toInt(value any, description string) (i int, err error) {
+	if valueInt64, ok := value.(int64); ok {
+		i = int(valueInt64)
+	} else {
+		err = fmt.Errorf("%s expected integer, got %T (%v)", description, value, value)
+	}
+	return
+}