rebol []

num: charset [ #"0" - #"9" #"." ]

view layout [
	f1: field
	f2: field

	button "valdate" [
		either parse f1/text [ some num end ][
			if error? err: try [
				decimal? load f1/text
			][
				alert "Not decimal value in field"
			]
		][
			alert "Non numeric characters in field"
		]
	]
]