/*
* Authors: k.inaba
* License: NYSL 0.9982 http://www.kmonos.net/nysl/
*
* Parser for Polemy programming language
*/
module polemy.parse;
import polemy._common;
import polemy.lex;
import polemy.ast;
import std.bigint;
/// Parsing Failure
class ParserException : Exception
{
private:
this(string msg) { super(msg); }
static ParserException create(Lexer)(Lexer lex, string msg)
{
return new ParserException(sprintf!"[%s] %s"(
lex.empty ? "EOF" : to!string(lex.front.pos), msg));
}
}
/// Named Constructor of Parser
auto parserFromLexer(Lexer)(Lexer lex)
{
return new Parser!Lexer(lex);
}
/// Named Constructor of Parser (just fwd to lexerFromString)
auto parserFromString(T...)(T params)
{
return parserFromLexer(polemy.lex.lexerFromString(params));
}
/// Named Constructor of Parser (just fwd to lexerFromFile)
auto parserFromFile(T...)(T params)
{
return parserFromLexer(polemy.lex.lexerFromFile(params));
}
/// Parser
class Parser(Lexer)
{
this(Lexer lex)
{
this.lex = lex;
}
Program parseProgram()
{
Program p;
while( !lex.empty )
p ~= parseStatement();
return p;
}
Statement parseStatement()
{
auto saved = lex.save;
scope(failure) lex = saved;
if( lex.empty )
throw new ParserException("EOF during parsing a statement");
auto pos = lex.front.pos;
if( lex.front.kind==Token.Kind.identifier && lex.front.str=="var" )
{
// "var" Var "=" Expression ";"
lex.popFront;
string var = lex.front.str;
lex.popFront;
eat("=", "for variable declaration");
auto parsed = new DeclStatement(pos, var, parseExpression());
eat(";", "after variable declaration");
return parsed;
}
else
{
// Expression ";"
auto parsed = new ExprStatement(pos, parseExpression());
eat(";", "after statement");
return parsed;
}
}
Expression parseExpression()
{
auto saved = lex.save;
scope(failure) lex = saved;
// Expr ::= E0
// E0 ::= (E1 "=")* E1
// E1 ::= (E2 "+"|"-")* E2
// E2 ::= (E3 "*"|"/")* E3
// E3 ::= int | str | id | "(" Expr ")"
return parseE0();
}
Expression parseE0()
{
auto lhs = parseE1();
if( tryEat("=") )
lhs = new BinOpExpression(lhs.pos, "=", lhs, parseE0());
return lhs;
}
Expression parseE1()
{
for(auto lhs = parseE2();;)
{
if( tryEat("+") )
lhs = new BinOpExpression(lhs.pos, "+", lhs, parseE2());
else if( tryEat("-") )
lhs = new BinOpExpression(lhs.pos, "-", lhs, parseE2());
else
return lhs;
}
}
Expression parseE2()
{
for(auto lhs = parseE3();;)
{
if( tryEat("*") )
lhs = new BinOpExpression(lhs.pos, "*", lhs, parseE3());
else if( tryEat("/") )
lhs = new BinOpExpression(lhs.pos, "/", lhs, parseE3());
else
return lhs;
}
}
Expression parseE3()
{
if( lex.empty )
throw new ParserException("EOF during parsing an expression");
auto pos = lex.front.pos;
if( lex.front.kind == Token.Kind.number )
{
scope(exit) lex.popFront;
return new IntLiteralExpression(pos, BigInt(cast(string)lex.front.str));
}
if( lex.front.kind == Token.Kind.stringLiteral )
{
scope(exit) lex.popFront;
return new StrLiteralExpression(pos, lex.front.str);
}
if( tryEat("(") )
{
auto e = parseE0();
eat(")", "after parenthesized expression");
return e;
}
scope(exit) lex.popFront;
return new VarExpression(pos, lex.front.str);
}
private:
Lexer lex;
void eat(string kwd, lazy string msg)
{
if( !tryEat(kwd) )
{
auto e = ParserException.create(lex, "'"~kwd~"' is expected "~msg~" but '"
~(lex.empty ? "EOF" : lex.front.str)~"' occured");
throw e;
}
}
bool tryEat(string kwd)
{
if( lex.empty || lex.front.kind!=Token.Kind.identifier || lex.front.str!=kwd )
return false;
lex.popFront;
return true;
}
}
unittest
{
auto p = parserFromString(`
var x = 100;
var y = 200;
`);
Program prog = p.parseProgram();
assert( prog.length == 2 );
auto p0 = cast(DeclStatement)prog[0];
auto p1 = cast(DeclStatement)prog[1];
assert( p0.var == "x" );
assert( p1.var == "y" );
assert( (cast(IntLiteralExpression)p0.expr).data == 100 );
assert( (cast(IntLiteralExpression)p1.expr).data == 200 );
}
unittest
{
auto p = parserFromString(`
var zzz = 100; # comment
zzz = zzz + zzz * "fo\no"; # comment
42;
`);
auto s0 = new DeclStatement(null, "zzz", new IntLiteralExpression(null, BigInt(100)));
auto s1 = new ExprStatement(null, new BinOpExpression(null, "=",
new VarExpression(null, "zzz"),
new BinOpExpression(null, "+",
new VarExpression(null, "zzz"),
new BinOpExpression(null, "*",
new VarExpression(null, "zzz"),
new StrLiteralExpression(null, "fo\\no")
))));
auto s2 = new ExprStatement(null, new IntLiteralExpression(null, BigInt(42)));
Program prog = p.parseProgram();
assert( prog.length == 3 );
assert( prog[0] == s0 );
assert( prog[1] == s1 );
assert( prog[2] == s2 );
}