1.2. Term signaturesΒΆ

The signature section of a DynSem module provides definitions for program terms and for additional entities used in the specification of a language’s dynamic semantics. We discuss here the subsections of signature which deal with representation of terms.

Note

For a discussion of signature subsections dealing with operational concepts see Signatures of arrows, components and meta-functions.

sorts

Define sorts of program and value terms, separated by white space. For example:

sorts Exprs Stmts

DynSem has a number of built-in sorts and operations on them: String, Int, List, etc. For a complete list and description of operations available see Built-in data types.

constructors

Define constructors for program and value terms. There are two constructor variants:

regular constructors

Define regular constructors. Definitions take the form NAME: {SORT “*”}* -> SORT, where NAME is the name of the constructor, followed by the sorts of the children of the constructor, and where the last SORT is the sort of the constructor. Example:

constructors
  Plus: Exprs * Exprs -> Exprs
implicit constructors

Define unary constructors which can be implicitly constructed/deconstructed in pattern matches and term constructions. For example, the constructor:

constructors
  OkV: V -> O {implicit}

declares the OkV unary constructor. In term constructions where a term of sort O is expected but a term t of sort V is provided, the constructor OkV is automatically constructed to surround term t to become Ok(t). In pattern matches where a term of sort O is provided but a term of sort V is expected, a pattern match for the term OkV is automatically inserted.

sort aliases

Declare sort synonyms. Sort aliases are useful to define shorthands for composed sorts such as for Maps and Lists. For example:

sort aliases
  Env = Map(String, Value)
  SciNum = (Float * Int)

declares Env as a sort alias for Map(String, Value). Wherever the sort Map(String, Value) is used, the alias Env can be used instead. The example also declares SciNum as a sort alias for the pair of a Float and an Int.

Note

sort-aliases are only syntactic sugar for their aliased sorts and sorts can therefore not be distinguished based on name. For example if two sort aliases Env1 and Env2 are defined for Map(String, Value) they all become equal and there is no type difference between Env1 and Env2. One can now see Env1 = Env2 = Map(String, Value).

variables

Defines variable prefix schemes. Variable schemes take the form ID = S and express the expectation that all variables prefixed with ID are of the sort S. A variable is part of the scheme X if it’s name begins with X and is either followed only by numbers and/or apostrophes, or is followed by _ followed by any valid identifier. For example given the scheme:

variables
  v : Value

the following are valid variable names: v1, v2, v’, v’‘’, v1’, v_foo.

Note

Variable schemes can be useful in combination with dynsem implicit reductions to concisely express the expected sort.

native datatypes

These define datatypes implemented natively (in Java) which can be used inside DynSem specifications.

Error

Not documented