3º. 2º cuatrimestre. Itinerario de Computación. Grado en Ingeniería Informática. ULL
Diseñe un lenguaje de programación sencillo (Sintáxis convencional a la C/BASIC/JavaScript/…). Escriba un analizador sintáctico descendente recursivo (PDR) que genere árboles de análisis abstracto que conformen a los usados por el intérprete del lenguaje Egg.
* y + dentro de la gramática para indicar repeticionesif,condiciones como a <= b,asignaciones,funciones y llamadas a funciones,Quizá la opción mas sencilla sea empezar con un lenguaje basado en Niklaus Wirth’s PL/0 y -si se dispone de tiempo - irlo extendiendo hacia mini-pascal.
Veamos un ejemplo basado en PL/0:
expressions → expression
| 'begin' expression (SENTENCE_SEPARATOR expression)* 'end'
expression → 'if' expression 'then' expressions
| 'if' expression 'then' expressions 'else' expressions
| 'while' expression 'do' expressions
| 'func' ID '(' (ID ',')* ID? ')' expressions
| 'func' '(' (ID ',')* ID? ')' expressions
| 'let' ID '=' expression
| 'set' ID '=' expression
| 'call' ID '(' (expression ',')* expression ')'
| 'call' ID '(' ')'
| comparison
comparison → sum (COMPOP sum)*
sum → factor (ADDOP factor)*
factor → unary (MULOP unary)*
unary → UNARYOP ? operand
operand → ID
| NUM
| STRING
| BOOLEAN
| '(' expression ')'
En XRegExp, dobles escapes:
WHITES = `\\s+ | #.*`
SENTENCE_SEPARATOR = `[;]`
NUM = `
\\d+ # Can have integer digits
\\.? # Can have decimal point
\\d* # Can have decimal digits
(
[eE] # Can have exponents
[-+]?\\d+ # Exponents numbers can have sign
)?`
STRING = `
"( # Has to start with double quote "
(
[^\\"] # Anything that is not a slash nor double quote "
| \\. # Or anything escaped
)* # Zero or more times
)" # Has to end with double quote "`
BOOLEAN = `(true | false)`
OPERATORS =`
(
\\b( and | or | not )\\b
| == | != | <= | >= | < | > | [+] | - | [*] | [/] | %
)
`, 'xy');
RESERVED_WORDS = `
(
\\b( true | false | begin | end | if | then | else | while | do | func | let | set | call )\\b
)`
ID = `[a-zA-Z]\w*` # An identifier
Below you can see an infix program that declares an array with 4 elements. Prints the array, the length of the array, the string resulting of calling the join method of the array and the array resulting of calling the map method to return an array formed with the double of each element
begin
# array is an egg function that returns an array
let result = call array(2, 3, 4, 5);
# print is also egg function
call print(result);
# We can also access array properties
call print("Array length: " + result.length);
# And call array methods
let string = call result.join(" ~ ");
call print(string);
# We can use array map method by passing an anonymous function as argument
let doubles = call result.map(func(x, i, a) begin
x * 2
end);
call print(doubles)
end
Execution of examples/arrays.inf
bin/infix2egg.js --run examples/arrays.inf
And the result is
[ 2, 3, 4, 5 ]
Array length: 4
2 ~ 3 ~ 4 ~ 5
[ 4, 6, 8, 10 ]
Another example:
begin
let variable = if "string" != "string" then 2 else 3
end
Usage: infix2egg [options]
Options:
-V, --version output the version number
-r --run <fileName> compiles the input infix program and runs it using the egg interpreter
-c --compile <fileName> compile the infix program to produce a JSON containing the input egg AST
-i --interpret <fileName> interprets the egg AST
-p --plugins [plugin1:plugin2:...:pluginK] specify infix/egg plugins
-h, --help output usage information
A la hora de escribir el ejecutable que hace la traducción se encontrará con el problema de parsear la línea de comandos. Puede usar el módulo commander para ello
Dado que esta práctica esta en un repo y su intérprete de egg está en otro repo, tenemos que resolver el problema de las “dependecias externas”. Podríamos usar submódulos git pero en este caso como tenemos publicado en github-registry nuestro intérprete egg lo usaremos en nuestro compilador del lenguaje infijo que hemos diseñado
El ejemplo que sigue muestra soluciones a estos problemas:
[~/…/crguezl-infix2-egg(master)]$ cat bin/infix2egg.js
#!/usr/bin/env node
const fs = require('fs');
const commander = require('commander');
const { egg } = require('@XXXXXXXXXX/egg');
const { parseFromFile } = require('../lib/parseFile');
commander
.version(require('../package.json').version)
.option('-r --run <fileName>', 'compiles the input infix program and runs it using the egg interpreter')
.option('-c --compile <fileName>', 'compile the infix program to produce a JSON containing the input egg AST')
.option('-i --interpret <fileName>', 'interprets the egg AST')
.option('-p --plugins [plugin1:plugin2:...:pluginK]', 'specify infix/egg plugins', val => val.split(':'))
.parse(process.argv);
// Execute plugins
if (commander.plugins) {
commander.plugins.forEach(require);
}
// Compile and interpret
if (commander.run) {
const ast = JSON.stringify(parseFromFile(commander.run));
egg.interpretFromPlainAst(ast);
}
// Run the parser to produce the EGG AST from the infix program
else if (commander.compile) {
const outputPath = `${commander.compile}.egg.evm`;
const ast = parseFromFile(commander.compile);
fs.writeFileSync(outputPath, JSON.stringify(ast, null, '\t'));
}
// Interpret
else if (commander.interpret) {
egg.runFromEVM(commander.interpret);
}
// Show help
else {
commander.help();
}
[~/.../eval/lucas(casiano)]$ pwd -P
/Users/casiano/campus-virtual/1819/pl1819/introduccion/tema3-analisis-descendente-predictivo-recursivo/practicas/p8-t3-pdr-infix2egg/eval/p8-t3-pdr-infix2eg-alu0101042305