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algebraic data types and traits

TLDR

• algebraic data types and catchall for nims type system

links

• [type classes](https://nim-lang.org/docs/manual.html#generics-type-classes
• implicit generics
• type bound operators
• object variants

TODOs

• read through the scala notes and try to replicate the algebraic DTs
• move all the type logic stuff in here
• create a test file
• add readme
• add to bookofnim
• metatype examples
• type bound operator examples (and should probably reread those docs)
• probably should reread the typedesc docs
• symbol lookups in generics
  • mixin statement
  • bind statement
  • delegating bind statements
• object variants: reread the docs
  • using the dereferencing operator to reassign a case objects fields after instantiation
  • differences with case + elif branches in the case statement
  • enums vs range type for the discrimator field
• generics and the method call syntax
  • theres a [:X] syntax that doesnt conflict with the method call syntax (blah.method)
    • docs
    • forum post

metatypes

• untyped lookup symbols & perform type resolution after the expression is interpreted & checked
  • i.e. expression is lazily resolved to its value (for templates)
  • use to pass a block of statements
• typed: semantic checker evaluates and transforms args before expression is interprted & checked
  • an expression that is eagerly resolved to its value (for templates)
  • i.e. whenever u set a type in a signature its resolved immediately
• typedesc a type description
• void absence of any type, generally used as proc return type

type bound operators

• a proc or func whose name starts with = but isnt an operator
• unrelated to propertie setters which end in = despite syntax similarities
  • x =copy y
  • x =destroy y Generic destructor implementation
  • x =sink y Generic sink implementation
  • x =trace y Generic trace implementation

type classes

• pseudo type that can be used to match via the is operator
• object, tuple, enum, proc, ref, ptr, var, distinct, array, set, seq auto
• in addition, every generic type creates a type class of the same name

typedesc

• since nim treats the names of types as regular values in certain contexts in the compilation phase
• typedesc is a generic type for all types denoting the type class of all types
• procs using typedesc params are implicitly generic

object variants

• preferred over an object hierarchy with multiple levels when simple variants suffice
• are tagged unions, which use an enum to discrimate between variant
  • generally a field called kind is set to SomeEnum, whose fields determine the branch
• also called case objects in the docs

variant pragmas

• uncheckedAssign disables re-assignment restrictions

generics

• abc