Updated Programming language specification (Gemstone) (markdown)

Programming-language-specification-(Gemstone).md

@@ -1,3 +1,51 @@
 # Programming language specification
 
-`TODO: write language specification`
+## Primitive data types
+The most fundamental types of data. They provide the base upon everything else is built. A primitive type has 2 properties: size in bytes and arithmetic model (additionally specifies representation on bit level). There are exactly two primitive data types:
+
+| Type name | size in bytes | arithmetic model |
+| - | - | - |
+| `int` | 4 | signed integer stored as two's complement with the MSB representing the sign bit |
+| `float` | 4 | signed single precision floating point as specified by IEEE-754 |
+
+## Composite data types
+Primitive data types provide the foundation upon which direct derivations can be built. The derivations of primitive types we call composite types. A composite type modifies or extends the definition of a primitive or another composite type.
+Extensions or modifications can mean adding or removing a sign bit, exchanging the arithmetic model, etc.
+The declaration of a composite data type is made with the following syntax:
+
+`typedef <sign> <scale> <base> $name`
+
+### Sign
+The `<sign>` is a keyword specifying whether to implement a sign bit or not. Possible values are:
+- `signed`: for a single sign bit
+- `unsigned`: for no sign bit
+
+### Scale
+`<scale>` describes the scaling factor to use. This is a rational factor used alongside the byte size of the base. To calculate the final size of the composite type multiply all factors with the base types size in bytes.
+
+#### Possible values
+| Name | Factor |
+| - | - |
+| short | $2^{-1}$ |
+| long | $2$ |
+| half | $2^{-1}$ |
+| double | $2$ |
+
+#### Examples:
+IEEE-754 double precision floating point: `long float` with size: `4 bytes * 2 = 8 bytes` <br>
+32-Bit integer: `half long int` with size: `4 bytes * 2 * 2^(-1) = 4 bytes` <br>
+A single byte: `half short int` with size: `4 bytes * 2^(-1) * 2^(-1) = 1 byte` <br>
+
+#### Limitations:
+The size of composite type cannot exceed 32 and be lower than 1 nor be a non integral value.
+A notable exception is the primitive type `float`. Its size is constrained to 2, 4, 8, 10, 16 and 32 in order to remain compliant with the IEEE-754 standard. A platform may choose to only provide implementations for only a few of the previously named sizes. On x86 and x64 and ARM the most common composite floats are of the sizes: 4 (float) and 8 (double).
+
+### Base
+The base of a composite type specifies on which primitive or composite type a derivation is to be built.
+
+## Example types
+```cpp
+typedef long float double_precision
+typedef short short int ascii
+typedef double int long_int
+```