Literal values can be used anywhere in an expression that a variable or attribute name can be used.
String-types (including dates) are surrounded by single quotes (apostrophes); double quotation marks are not valid in SML.
Numeric types are not quoted.
Literals can contain quote characters. These need to be escaped by being preceded by a \.
For example:
local
days : string;
end_local;
days := '\'mon\',\'tue\',\'wed\',\'thurs\',\'fri\',\'sat\',\'sun\'';