Types.org

* Types
- GF is statically typed:
  You cannot say something like
  ...
  a = 3 ;
  a = "Foo" ;
  ...
- GF makes a distinction into abstract syntax/concrete syntax as well as resource modules

*** Basic types
- GF also support some basic types
  - Python has strings (called `str`). GF has strings (called `Str`).
  - Python has integers (called `int`). GF has integers (called `Int`).
  - Python has floating-point numbers (called `float`). GF's are called `Float`.
- These types can be used in resource modules and concrete syntax files
- Strings vs. String tuples
  - Substrings can be concatenated with *+*
  - Sentences in GF are kind of lists of strings, *++* concatenates lists of strings
- Example: 
  #+INCLUDE: "src/SimpleTypes.gf" src gf
  
*** Enumeration types
- The only kind of enumeration types in GF are the so-called *param* types

- Example: 
  #+INCLUDE: "src/Param.gf" src gf

*** Compound types
- GF has three kinds of compound types, tables, records and tuples, Python has dictionaries, tuples and lists
- GF does not really have lists
- Keys in tables usually are *param*s and keys in records are literal identifier

- Example: 
  #+INCLUDE: "src/Compound.gf" src gf

- To select values from tables the *!* operator is used, to select from records the *.* operator
- Tuples are special cases of records

*** Functions
- GF supports both regular functions and anonymous functions

- Example: 
  #+INCLUDE: "src/Functions.gf" src gf