Difference between revisions of "Attribute Grammars/Exercise 2: Numbers"
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(→Attribute grammar using only synthesized attributes) |
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<tr> | <tr> | ||
<td align="right">s</td> | <td align="right">s</td> | ||
| − | <td align="left"> | + | <td align="left">→</td> |
<td align="left"><em>symbol</em> <sub>1</sub> <strong>#</strong> <em>symbol</em> <sub>2</sub></td> | <td align="left"><em>symbol</em> <sub>1</sub> <strong>#</strong> <em>symbol</em> <sub>2</sub></td> | ||
<td align="left">{</td> | <td align="left">{</td> | ||
| Line 38: | Line 38: | ||
<tr> | <tr> | ||
<td align="right"><em>symbol</em> <sub>1</sub></td> | <td align="right"><em>symbol</em> <sub>1</sub></td> | ||
| − | <td align="left"> | + | <td align="left">→</td> |
<td align="left"><em>symbol</em> <sub>2</sub> <strong>dig</strong></td> | <td align="left"><em>symbol</em> <sub>2</sub> <strong>dig</strong></td> | ||
<td align="left">{</td> | <td align="left">{</td> | ||
| Line 66: | Line 66: | ||
<tr> | <tr> | ||
<td align="right"><em>symbol</em></td> | <td align="right"><em>symbol</em></td> | ||
| − | <td align="left"> | + | <td align="left">→</td> |
<td align="left"><strong>dig</strong></td> | <td align="left"><strong>dig</strong></td> | ||
<td align="left">{</td> | <td align="left">{</td> | ||
Revision as of 11:57, 2 May 2024
Considere a seguinte gramática atributiva:
| s | → | symbol 1 # symbol 2 | { | |
| s. val = symbol 1. val + symbol 2. val | ||||
| symbol 1. x = 1 | ||||
| symbol 2. x = 1 | ||||
| } | ||||
| symbol 1 | → | symbol 2 dig | { | |
| symbol 2. x = symbol 1. x * 5 | ||||
| symbol 1.val = symbol 2.val + dig.val * symbol 1.x | ||||
| } | ||||
| symbol | → | dig | { | |
| symbol.val = dig.val * symbol.x | ||||
| } |
O elemento lexical dig representa um dígito de 0 a 9, e o seu atributo val representa o valor numérico correspondente.
- Represente a àrvore semântica para a entrada 328#37.
- Apresente uma gramática atributiva equivalente que apenas contenha atributos sintetizados.
Solution
Semantic tree and dependency graph
"x" is an inherited attribute (propagation in blue); "val" is a synthesized attribute (propagation in red).
Attribute grammar using only synthesized attributes
We start by noting that the semantic computed by the previous grammar corresponds to base 5-like numbering (although the digits do not belong to base 5).
The new grammar is trivial to write (_1 and _2 are subscripts to differentiate instances of "symbol"):
s -> symbol_1 # symbol_2 { s.val = symbol_1.val + symbol_2.val }
symbol_1 -> symbol_2 dig { symbol_1.val = symbol_2.val * 5 + dig.val }
symbol -> dig { symbol.val = dig.val }
"val" is a synthesized attribute (propagation in red).
