Values and Types

Values in Feersum are all CIL objects. Value types are generally boxed types. The empty list is represented by null.

• Values and Types
  • Boolean
    • Implementation status
  • Vector
    • Implementation Status
  • Bytevector
    • Implementation status
  • Char
    • Implementation status
  • Null
    • Implementation status
  • Number
    • Implementation Status
  • Pair
    • Implementation Status
  • Port
    • Implementation status
  • Procedure
    • Implementation Status
  • String
    • Implementation Status
  • Symbol
    • Implementation status

Boolean

Booleans can be created with #t, #true, #f, and #false.

Implementation status

Booleans are represented as boxed bool instances of System.Boolean.

Vector

Vector literals are contiguous array types. Vectors are lists prefixed by #(. e.g.: #(123 456 789).

Implementation Status

Vectors are represented as object[] instances.

Bytevector

Byte vector literals are similar to vectors but contain arrays of byte values. Byte vectors are lists prefixed by #u8(. e.g.: #u8(0 10 5).

Implementation status

Byte vectors are represented as byte[] instances.

Char

Characters are single textual characters. Character literals consist of a #\ followed by a literal character or character name. Arbitrary unicode values can also be encoded as #\x followed by a hexedecimal character value.

Implementation status

Characters are represented as boxed char types. This means Unicode code points outside the BMP cannot be properly handled as character values. It’s unclear if characters should appear as UTF-32 code units or not.

Null

Null, or the empty list, is represented as ().

Implementation status

Null is represented by the CIL null value.

Number

Numbers in scheme form a “tower of sub-types”. There are several different numeric types any of which may be supported, however the relationship between them must be consistent.

The tower is:

• number
• complex number
• real number
• rational number
• integer

Number literals can be either integer or floating point literals, or constant values defined in other bases such as #x for hex and #o for octal.

Implementation Status

Inexact numbers are the only supported number type right now. All numbers are represented as boxed double instances of System.Double. Only floating point or integer literals are supported.

Pair

Pairs, or “cons pairs” are the building block of lists. Pairs are represented as (<car> . <cdr>) where <car> is the ‘left hand’ or ‘head’ of the pair and <cdr> is the ‘right hand’ or ‘tail’ portion.

Implementation Status

Cons pairs are impemented in the runtime. Cons pair literals are not yet supported.

Port

Ports are used for reading and writing data. The obvious choice for them would be some form of wrapper around streams.

Implementation status

Ports are not yet supported.

Procedure

Procedures are callable values. New procedures can be introduced with lambda define speical forms.

Implementation Status

In Feersum procedures follow a ‘unified calling convention’ of passing all arguments as a single CIL array of objects. Procedures are repsonisble for unpacking their own arguments and raising errors as appropriate.

When lambda defintiions are used to create procedures a ‘thunk’ is generated which unpacks the arguments into the target’s parameters. Lambda values are passed around as System.Func<object[], objec> instances.

String

Strings are arrays or sequences of characters. String literals are enclosed in ". Characters can also use hexedecimal or character escapes \ foloowed by a character or character name, or \x followed by a hex literal followed by ;.

Implementation Status

Strings are represented as .NET String instances. String literals and character escapes are supported. Not all Unicode characters can be specified in character escapes due to the UTF-16 reprensetaion of characters used in .NET.

Symbol

Symbols are quoted identifiers. Symbols behave like interned strings.

Implementation status

Symbols are instances of the Ident type.