Mythryl supports both alphabetic identifiers like in and non-alphabetic identifiers like ++. In general Mythryl does not distinguish between them semantically; either may be used to name a function, and either may be used as an infix operator. Whether a given identifier is infix or not is controlled not by their syntax but rather by using statements like:
infix my ++ ; # Make '++' infix, left-associative.
infixr my ++ ; # Make '++' infix, right-associative.
nonfix my ++ ; # Make '++' not infix.
infix my in ; # Make 'in' infix, left-associative.
infixr my in ; # Make 'in' infix, right-associative.
nonfix my ++ ; # Make 'in'not infix.
Like C and most contemporary languages, Mythryl is syntactically case sensitive: foo, Foo and FOO are three separate identifiers.
Unlike C and most contemporary languages, Mythryl is also semantically case sensitive:
foo # Variable, function or package name.
Foo # Type or API name.
FOO # enum constant / datatype constructor.