[QUESTION] Using Expr.Function with function type arguments

[talvez-euovictor]

Hi @antonmedv!

I'm trying to port some of the functions provided by the lo package to have more capabilities of collection types manipulation. But I'm having a hard time trying to represent the function argument as an expression. It compiles but throws a runtime error.

Expr version: v1.17.5
Go version: go1.24.9 linux/amd64

Example of the Expr function:

import (	"github.com/expr-lang/expr"	"github.com/samber/lo" ) const sliceToMapFuncParamsLen = 2 func sliceToMapFunc() expr.Option {	return expr.Function(	"SliceToMap",	func(params ...any) (any, error) {	if len(params) != 2 {	return nil, invalidParametersNumberError("SliceToMap", sliceToMapFuncParamsLen, len(params))	}	slice, ok := params[0].([]any)	if !ok {	return nil, invalidParameterTypeError("SliceToMap", 0, "[]any", TypeOf(params[0]))	}	fn, ok := params[1].(func(any) (string, any))	if !ok {	return nil, invalidParameterTypeError("SliceToMap", 1, "func(any) (string, any)", TypeOf(params[1]))	}	return lo.SliceToMap(slice, fn), nil	},	new(func([]any, func(any) (string, any)) (any, error)),	) } 

Expression examples:

SliceToMap(.data, {{string(#.key):#.value}}) SliceToMap(.data, {#.key,#.value}) 

[antonmedv]

This {#.key,#.value} is not a function. This is a predicate. Only afavialable only inside map/function and other builtins. It's not avialble for custom functions.