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Dmitry Boulytchev 2018-03-28 15:01:04 +03:00
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@ -121,7 +121,7 @@ Procedures are unit-returning functions. We consider adding procedures as a sepa
essential redefinition of the semantics for expressions; at the same time the code generation for funictions is a little trickier, than for procedures, so essential redefinition of the semantics for expressions; at the same time the code generation for funictions is a little trickier, than for procedures, so
it is reasonable to split the implementation in two steps. it is reasonable to split the implementation in two steps.
At the source level the procedures are added as a separate syntactic category~--- definition $\mathscr D$: At the source level procedures are added as a separate syntactic category~--- definition $\mathscr D$:
\[ \[
\begin{array}{rcl} \begin{array}{rcl}
@ -130,7 +130,7 @@ At the source level the procedures are added as a separate syntactic category~--
\end{array} \end{array}
\] \]
In other words, a definition is a (possibly empty) sequence of procedure description. Each description consists of the a name of the procedure, a In other words, a definition is a (possibly empty) sequence of procedure descriptions. Each description consists of a name for the procedure, a
list of names for its arguments and local variables, and a body (statement). In concrete syntax a single definition looks like list of names for its arguments and local variables, and a body (statement). In concrete syntax a single definition looks like
\begin{lstlisting} \begin{lstlisting}
@ -140,7 +140,7 @@ list of names for its arguments and local variables, and a body (statement). In
} }
\end{lstlisting} \end{lstlisting}
where $name$~--- a name for a procedure, $a_i$~--- its arguments, $l_i$~--- local variables, $s$~--- body. where $name$~--- a name for the procedure, $a_i$~--- its arguments, $l_i$~--- local variables, $s$~--- body.
We also need to add a call statement to the language: We also need to add a call statement to the language:
@ -160,7 +160,7 @@ Finally, we have to redefine the syntax category for programs at the top level:
\mathscr L = \mathscr D\mathscr S \mathscr L = \mathscr D\mathscr S
\] \]
In other words, we extended a statement with a set of definitions. In other words, we extend a statement with a set of definitions.
With procedures, we need to introduce the notion of \emph{scope}. When a procedure is called, its arguments With procedures, we need to introduce the notion of \emph{scope}. When a procedure is called, its arguments
are associated with actual parameter values. A procedure is also in ``posession'' of its local variables. are associated with actual parameter values. A procedure is also in ``posession'' of its local variables.
@ -216,8 +216,8 @@ Finally, we need two transformations for states:
\end{array} \end{array}
\] \]
The first one simlulates the entering the new scope with a set of local variables $S$; the second one simulates the leaving The first one simlulates entering the new scope with a set of local variables $S$; the second one simulates leaving
from inner scope (described by the first state) to outer one (described by the second). from an inner scope (described by the first state) to an outer one (described by the second).
\setarrow{\xRightarrow} \setarrow{\xRightarrow}
@ -248,7 +248,7 @@ In order to support procedures and calls, we enrich the stack machine with three
\] \]
Informally speaking, instruction \llang{BEGIN} performs entering into the scope of a procedure; its operands are the lists of argument names and Informally speaking, instruction \llang{BEGIN} performs entering into the scope of a procedure; its operands are the lists of argument names and
local variables; \llang{END} leaves the scope and returns to the call site, and \llang{CALL} performs the call. local variables; \llang{END} leaves the scope and returns to the call site, and \llang{CALL} performs the call itself.
We need to enrich the configurations for the stack machine as well: We need to enrich the configurations for the stack machine as well: