Umo programming language

Concept

• Effect system (not implemented)
• Subtyping (not implemented)
• Opt-in shared mutability (not implemented)
• Gradual typing (not implemented)

Expressions

Comment (not an expression though)

Currently // comment is implemented

Primary

• Parentheses: 1 + (2 + 3)
• Identifiers
• Numbers

Primary -- Identifiers

Currently /[a-zA-Z_][a-zA-Z_0-9]*/

Primary -- Numbers

• Decimal integer: /\d+/ (octal-like numbers like 018 may be forbidden later)
• Hexadecimal integer (not implemented)
• Octal integer (not implemented)
• Binary integer (not implemented)
• Decimal floating-point number /\d+\.\d+/

Call/Member expressions

• Call expressions: foo(bar, baz)
• Member expressions: foo.bar (not implemented)

Call/Member expressions -- Call expressions

• Empty arguments: foo()
• Non-empty arguments: foo(bar, baz)
• Trailing comma: foo(bar, baz,)

Operators

• Additive: +, - (Only + is implemented now)
• Multiplicative: *, / (not implemented)
• Relational: <, <=, >, >= (not implemented)
• Equality: ==, != (not implemented)
• Logical: &&, || (not implemented)
• Bitwise: &, |, ^ (not implemented)
• Shift: <<, >> (not implemented)
• Unary: -, ! (not implemented)

Note on types:

• Arithmetic operators: different types cannot be mixed together.

Closures

• Closure: |x| x * 2 (not implemented, subject to change)

Statements

Expression statements

Expression + ; is an expression statement.

(; may be auto-inserted in the future)

Let statements

let <ident> = <expr>;
let <ident>: <type> = <expr>;

The identifiers are in scope after the statement.

Scoping

The expression in the let statement can reference variables declared before the statement. Especially, it cannot reference variables declared in the statement itself.

// error
let f = |x| f(x);

This rule is not implemented yet and subject to change.

Types

• Primitive types: int, f64, ... (only int and f64 are implemented now)
• Placeholder type called Ambiguous (Ambiguous<Lo, Up>) ... corresponds with any in TS.
  • the corresponding syntax is not implemented yet.
• TBD

Development

Concept:

• Document-first
• Test-first

Prototype will be written in TypeScript