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Quellcode-Bibliothek© Kompilation durch diese Firma[Weder Korrektheit noch Funktionsfähigkeit der Software werden zugesichert.]Datei: mash_eval.ML Sprache: VDMOriginal von: VDM© |
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\section{Informal Language Definition}
Below the abstract syntax of the language is given in VDM-SL. In order to keep the language simple, only Integer and Boolean types are defined. A program consists of a declaration part followed by a statement. \begin{vdm_al} module AST exports all definitions types Program :: decls : seq of Declaration stmt : Stmt; \end{vdm_al} A (variable) declaration consists of an identifier, an associated type and an optional initial value. \begin{vdm_al} Declaration :: id : Identifier tp : Type val : [Value]; \end{vdm_al} An identifier is a sequence of characters. In our language two types are known, Boolean and Integer. The two types of values in the language are modeled as the corresponding VDM-SL types {\tt bool} and {\tt int}. \begin{vdm_al} Identifier = seq1 of char; Type = <BoolType> | <IntType> ; Value = BoolVal | IntVal; BoolVal :: val : bool; IntVal :: val : int; \end{vdm_al} Our simple language only knows four kinds of statements: block statements, assignments, a conditional statement, a for-loop and a repeat-loop\footnote{A while loop was not part of the assignment, because it has served as a demonstrating example for loop semantics during the course. It is left as an exercise to the reader.}. \begin{vdm_al} Stmt = BlockStmt | AssignStmt | CondStmt | ForStmt | RepeatStmt; \end{vdm_al} A block statement consists of local variable declarations and a non-empty sequence of statements. \begin{vdm_al} BlockStmt :: decls : seq of Declaration stmts : seq1 of Stmt; \end{vdm_al} The left-hand side of an assignment is a variable, which is simply an identifier. The right-hand side is defined as an expression. \begin{vdm_al} AssignStmt :: lhs : Variable rhs : Expr; Variable :: id : Identifier; \end{vdm_al} An expression could be a binary expression, a value or a variable. A binary expression consists of a left-hand expression, an operator and a right-hand expression. \begin{vdm_al} Expr = BinaryExpr | Value | Variable; BinaryExpr :: lhs : Expr op : Operator rhs : Expr; \end{vdm_al} The numeric operators of the language are addition, subtraction, Integer-division, and multiplication. The Boolean operators are less-than, greater-then, equality, conjunction, and finally disjunction. \begin{vdm_al} Operator = <Add> | <Sub> | <Div> | <Mul> | <Lt> | <Gt> | <Eq> | <And> | <Or>; \end{vdm_al} A conditional if-statement consists of a guard predicate, the then- and else-branch. \begin{vdm_al} CondStmt :: guard : Expr thenst : Stmt elsest : Stmt; \end{vdm_al} The for-loop consists of an initial assignment to the loop-variable, followed by an expression, which defines the stop value of the loop-variable, and the statement to be repeated. It is allowed to modify the loop-v \begin{vdm_al} ForStmt :: start : AssignStmt stop : Expr stmt : Stmt; \end{vdm_al} Finally, the repeat-loop consists of the statement to be repeated and its stop condition. \begin{vdm_al} RepeatStmt :: repeat : Stmt until : Expr; end AST \end{vdm_al} ¤ Dauer der Verarbeitung: 0.16 Sekunden (vorverarbeitet) ¤ |
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