Abstract

syntax The algebraic definition of abstract syntax trees below can, more or less, be read as a BNF grammar. Emphatic brackets, [[: : : ]], indicate nodes in an abstract syntax tree. grammar: ffl Expression = Identifier "true" "false" [[ "" Identifier "." Expression ]] [[ Expression Expression ]] [[ "rec" Identifier "." Expression ]] [[ "if" Expression "then" Expression "else" Expression ]] . Action semantics reasoning about functional programs 3 ffl Identifier = [[ letter + ]] . 2.2. Semantic functions Action semantic descriptions are syntax-directed in the denotational style: compositional semantic functions map abstract syntax into meaning and are defined inductively by semantic equations. There is one universal semantic domain, namely action, the sort of actions. Actions are expressed in a notation that looks a little like informal English prose but, in fact, it is a completely formal combinator-based notation. The verbose notation should be suggestive of the meaning of th...

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