Mythryl requires all type names to be in Mixed_Case and all constructors to be in UPPER_CASE (with the sole exception of the list constructor ’!’). Combined with the requirement that all statements end with a semicolon, this allows concise type declarations.
Mythryl declares tuples using parentheses-and-commas syntax parallel to normal tuple construction syntax. This loses the tie to mathematical set product notation, but carries better C intuition and is more consistent with the way records types are declared in both SML and Mythryl:
My_Tuple = (Int, Float, String);
A simple sumtype declaration is now simply
Color = RED | GREEN | BLUE;
Declaring the same type opaque in an API (signature) is even more concise:
Color;
Mythryl does not use the SML of particle in sumtype declarations. (Mythryl returns of to the general identifier pool, reducing the reserved word count by one.)
Point = TWO_D (Float, Float) | THREE_D (Float, Float, Float);
Mythryl uses prefix type functions (“type constructors”), in contrast to SML’s postfix type syntax. A list of strings type is now:
List_Of_Strings = List(String);
Record and function type declarations are otherwise unchanged:
My_Record_Type = { name: String, age: Int };
My_Arrow_Type = List(Int) -> Int;
Mythryl type variables are typically single uppercase letters, canonically X Y Z:
Typeagnostic_Tuple(X, Y) = (List(X), Y, X -> Y);
Relative to SML type variable syntax 'a, the Mythryl
syntax carries better intuition to C programmers, and incidentally
frees up leading apostrophe to implement normal C-style character
constant syntax.
When more semantic content is needed, longer type variable names incorporating a single leading capital may be used:
Typeagnostic_Tuple(A_boojum, A_snark) = (List(A_boojum), A_snark, A_boojum -> A_snark);