Question

Given a CFG in BNF, (50 points)

<stmt_list> → <stmt> | <stmt>; <stmt_list>

<stmt> → <var> = <expr>

<expr> → <var> + <expr> | <var> * <expr> | <var>

<var> →a| b| c| d

1. show a derivation for the given sentence a = b*c - d; b = d - a

2. show a parsing tree for a = b*c - d; b = d - a

Answer 1

1)

<stmt_list>
<stmt>; <stmt_list>
<stmt>; <stmt>
<stmt>; <var> = <expr>
<stmt>; <var> = <var> - <expr>
<stmt>; <var> = <var> - <var>
<stmt>; <var> = <var> - a
<stmt>; <var> = d - a
<stmt>; b = d - a
<var> = <expr>; b = d - a
<var> = <var> * <expr>; b = d - a
<var> = <var> * <var> - <var>; b = d - a
<var> = <var> * <var> - d; b = d - a
<var> = <var> * c - d; b = d - a
<var> = b * c - d; b = d - a
a = b * c - d; b = d - a

b)

/ Stunt list 1 stat; stmt_list 2 stmt var= expr 1 1 expr expr 1 1 2 b Б vara expr b var expr :) var var ex a var var с C var d

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