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parse.cpp
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parse.cpp
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#include "parse.hpp"
#include "lex.hpp"
#include "error.hpp"
ASTNode Expression();
ASTNode Statement();
// when we know what token should come next, use this
// it throws an error if the expected token isn't next
Tokinfo expect( TokenID type ) {
auto tok = lex();
if ( tok.token != type )
error( tok.linenum, "expected token of type %s", token_to_string( type ) );
return tok;
}
// check if the next token could start an expression
bool is_expression_next() {
auto tok = lex();
unlex( tok );
return tok.token == TOKEN_BANG
|| tok.token == TOKEN_MINUS
|| tok.token == TOKEN_INT
|| tok.token == TOKEN_STRING
|| tok.token == TOKEN_ID
|| tok.token == TOKEN_LPAREN;
}
// there are certain places where semicolon insertion makes putting a newline
// there illegal cause a semicolon gets inserted. this function checks that
void check_for_bad_semicolon() {
auto tok = lex();
unlex( tok );
if ( tok.token != TOKEN_SEMICOLON ) return;
if ( tok.lexeme == "" )
error( tok.linenum, "unexpected newline" );
else
error( tok.linenum, "syntax error on \";\"" );
}
ASTNode newidentifier() {
auto tok = expect( TOKEN_ID );
return ASTNode ( AST_NEWID, tok.linenum, tok.lexeme );
}
ASTNode typeidentifier() {
auto tok = expect( TOKEN_ID );
return ASTNode ( AST_TYPEID, tok.linenum, tok.lexeme );
}
ASTNode Operand() {
auto tok = lex();
switch ( tok.token ) {
case TOKEN_INT: return ASTNode ( AST_INT, tok.linenum, tok.lexeme );
case TOKEN_STRING: return ASTNode ( AST_STRING, tok.linenum, tok.lexeme );
case TOKEN_ID: return ASTNode ( AST_ID, tok.linenum, tok.lexeme );
default: {
unlex ( tok );
expect( TOKEN_LPAREN );
auto result = Expression();
expect( TOKEN_RPAREN );
return result;
}
}
}
ASTNode Arguments() {
expect( TOKEN_LPAREN );
ASTNode result = { AST_ACTUALS };
// ExpressionList - at least one expression, but possibly more, all delimited by commas
if ( is_expression_next() ) {
auto expr = Expression();
result.add_child( expr );
Tokinfo tok;
while ( ( tok = lex() ).token == TOKEN_COMMA && is_expression_next() ) {
expr = Expression();
result.add_child( expr );
}
unlex( tok );
check_for_bad_semicolon();
// consume trailing comma in params list if there is one
if ( ( tok = lex() ).token != TOKEN_COMMA ) unlex( tok );
}
expect( TOKEN_RPAREN );
return result;
}
ASTNode UnaryExpr() {
auto tok = lex();
ASTNode result;
switch ( tok.token ) {
// logical not
case TOKEN_BANG: {
result = ASTNode ( AST_LOGIC_NOT, tok.linenum );
auto exp = UnaryExpr();
result.add_child( exp );
break;
}
// unary minus aka "take the negative"
case TOKEN_MINUS: {
result = ASTNode( AST_UMINUS, tok.linenum );
auto exp = UnaryExpr();
if ( exp.type == AST_INT && exp.lexeme[0] != '-' ) {
result = exp;
result.lexeme = "-" + result.lexeme;
} else
result.add_child( exp );
break;
}
default:
unlex( tok );
result = Operand();
while ( ( tok = lex() ).token == TOKEN_LPAREN ) {
unlex( tok );
auto left = result;
result = ASTNode( AST_FUNCCALL );
auto right = Arguments();
result.add_child( left );
result.add_child( right );
result.linenum = left.linenum;
}
unlex( tok );
break;
}
return result;
}
ASTNode MulExpr() {
ASTNode result = UnaryExpr();
Tokinfo tok;
// children are unary expressions, multiplied
while ( ( tok = lex() )
.token == TOKEN_STAR
|| tok.token == TOKEN_SLASH
|| tok.token == TOKEN_PERCENT ) {
auto right = UnaryExpr();
auto left = result;
result = ASTNode ( AST_UNSET, tok.linenum, tok.lexeme );
if ( tok.token == TOKEN_STAR ) result.type = AST_MUL;
if ( tok.token == TOKEN_SLASH ) result.type = AST_DIV;
if ( tok.token == TOKEN_PERCENT ) result.type = AST_MOD;
result.add_child( left );
result.add_child( right );
}
unlex( tok );
return result;
}
ASTNode AddExpr() {
ASTNode result = MulExpr();
Tokinfo tok;
// children are Mul expressions, added to each other
while ( ( tok = lex() ).token == TOKEN_PLUS || tok.token == TOKEN_MINUS ) {
auto right = MulExpr();
auto left = result;
result = ASTNode ( AST_UNSET, tok.linenum, tok.lexeme );
if ( tok.token == TOKEN_PLUS ) result.type = AST_PLUS;
if ( tok.token == TOKEN_MINUS ) result.type = AST_MINUS;
result.add_child( left );
result.add_child( right );
}
unlex( tok );
return result;
}
ASTNode RelExpr() {
ASTNode result = AddExpr();
Tokinfo tok;
// children are Add expressions, compared to each other
while ( ( tok = lex() )
.token == TOKEN_EQ
|| tok.token == TOKEN_NEQ
|| tok.token == TOKEN_GEQ
|| tok.token == TOKEN_LEQ
|| tok.token == TOKEN_LT
|| tok.token == TOKEN_GT ) {
auto right = AddExpr();
auto left = result;
result = ASTNode ( AST_UNSET, tok.linenum, tok.lexeme );
switch ( tok.token ) {
case TOKEN_EQ:
result.type = AST_EQ;
break;
case TOKEN_NEQ:
result.type = AST_NEQ;
break;
case TOKEN_GEQ:
result.type = AST_GEQ;
break;
case TOKEN_LEQ:
result.type = AST_LEQ;
break;
case TOKEN_LT:
result.type = AST_LT;
break;
case TOKEN_GT:
result.type = AST_GT;
break;
default:
// NOTE: this is actually unreachable:
// the condition for the loop enforces that tok.token
// is one of the six cases I check here, which can be
// easily verified by inspection
error( tok.linenum, "unreachable" );
}
result.add_child( left );
result.add_child( right );
}
unlex( tok );
return result;
}
ASTNode AndExpr() {
ASTNode result = RelExpr();
Tokinfo tok;
// children are relation/comparison Expressions, OR-ed together
while ( ( tok = lex() ).token == TOKEN_LOGIC_AND ) {
auto right = RelExpr();
auto left = result;
result = ASTNode ( AST_LOGIC_AND, tok.linenum, tok.lexeme );
result.add_child( left );
result.add_child( right );
}
unlex( tok );
return result;
}
ASTNode OrExpr() {
ASTNode result = AndExpr();
Tokinfo tok;
// children are And Expressions, OR-ed together
while ( ( tok = lex() ).token == TOKEN_LOGIC_OR ) {
auto right = AndExpr();
auto left = result;
result = ASTNode ( AST_LOGIC_OR, tok.linenum, tok.lexeme );
result.add_child( left );
result.add_child( right );
}
unlex( tok );
return result;
}
ASTNode Expression() {
return OrExpr();
}
ASTNode BreakStmt() {
auto tok = expect( TOKEN_BREAK );
return ASTNode ( AST_BREAK, tok.linenum, tok.lexeme );
}
ASTNode ReturnStmt() {
auto tok = expect( TOKEN_RETURN );
ASTNode result( AST_RETURN, tok.linenum, tok.lexeme );
// optional expression to return
if ( is_expression_next() ) {
auto exp = Expression();
result.add_child( exp );
}
return result;
}
ASTNode VarDecl() {
auto tok = expect( TOKEN_VAR );
ASTNode result ( AST_VAR, tok.linenum, tok.lexeme );
auto newid = newidentifier ();
auto typeident = typeidentifier();
result.add_child( newid );
result.add_child( typeident );
return result;
}
ASTNode Block() {
expect( TOKEN_LBRACE );
ASTNode result;
result.type = AST_BLOCK;
Tokinfo tok;
while ( ( tok = lex() ).token != TOKEN_RBRACE ) {
unlex( tok );
auto stmt = Statement();
result.add_child( stmt );
expect( TOKEN_SEMICOLON );
}
unlex( tok );
expect( TOKEN_RBRACE );
return result;
}
ASTNode IfStmt() {
auto tok = expect( TOKEN_IF );
ASTNode result( AST_IF, tok.linenum, tok.lexeme );
// Condition
{
auto expr = Expression();
result.add_child( expr );
}
check_for_bad_semicolon();
// block to execute if condition is true
{
auto blk = Block();
result.add_child( blk );
}
// if no else, we're done
if ( ( tok = lex() ).token != TOKEN_ELSE ) {
unlex( tok );
return result;
}
result.type = AST_IFELSE;
result.lexeme = "";
tok = lex();
unlex( tok );
// else -> lbrace = if/else
// else -> if = if/elseif i.e. another if statement
if ( tok.token == TOKEN_LBRACE ) {
auto blk = Block();
result.add_child( blk );
} else if ( tok.token == TOKEN_IF ) {
auto ifstmt = IfStmt();
result.add_child( ifstmt );
} else
error( tok.linenum, "syntax error o\"%s\"", tok.lexeme.data() );
return result;
}
ASTNode ForStmt() {
auto tok = expect( TOKEN_FOR );
ASTNode result( AST_FOR, tok.linenum );
tok = lex();
unlex( tok );
// [ Condition ]
if ( tok.token != TOKEN_LBRACE ) {
auto expr = Expression();
result.add_child( expr );
} else
result.add_child( { AST_ID, -1, "$true" } );
tok = lex();
unlex( tok );
check_for_bad_semicolon();
auto blk = Block();
result.add_child( blk );
return result;
}
ASTNode Statement() {
auto tok = lex();
unlex( tok );
switch ( tok.token ) {
case TOKEN_VAR:
return VarDecl();
case TOKEN_RETURN:
return ReturnStmt();
case TOKEN_BREAK:
return BreakStmt();
case TOKEN_LBRACE:
return Block();
case TOKEN_IF:
return IfStmt();
case TOKEN_FOR:
return ForStmt();
default:
if ( !is_expression_next() ) return { AST_EMPTYSTMT };
auto result = Expression();
// Assignment
if ( ( tok = lex() ).token == TOKEN_ASSIGN ) {
auto right = Expression();
auto left = result;
result = ASTNode ( AST_ASSIGN, tok.linenum, tok.lexeme );
result.add_child( left );
result.add_child( right );
if ( ( tok = lex() ).token == TOKEN_ASSIGN ) error( tok.linenum, "syntax error on \"=\"" );
} else {
auto tmp = result;
result = ASTNode( AST_EXPRSTMT, tmp.linenum );
result.add_child( tmp );
}
unlex( tok );
return result;
}
}
// "formal" in the reference compiler I think
ASTNode ParameterDecl() {
ASTNode result ( AST_FORMAL );
auto newid = newidentifier();
auto typeident = typeidentifier();
result.add_child( newid );
result.add_child( typeident );
return result;
}
ASTNode FunctionDecl() {
auto tok = expect( TOKEN_FUNC );
ASTNode result ( AST_FUNC, tok.linenum, tok.lexeme );
{
auto ident = newidentifier();
result.add_child( ident ); // FunctionName
}
expect( TOKEN_LPAREN );
// add signature
ASTNode sig ( AST_SIGNATURE );
ASTNode formals ( AST_FORMALS );
tok = lex();
unlex( tok );
// ParameterList
if ( tok.token == TOKEN_ID ) {
auto params = ParameterDecl();
formals.add_child( params );
// parameters delimited by commas
while ( ( tok = lex() ).token == TOKEN_COMMA
&& ( tok = lex() ).token == TOKEN_ID ) {
unlex( tok );
params = ParameterDecl();
formals.add_child( params );
}
unlex( tok );
check_for_bad_semicolon();
// consume trailing comma in params list if there is one
if ( ( tok = lex() ).token != TOKEN_COMMA ) unlex( tok );
}
expect( TOKEN_RPAREN );
sig.add_child( formals );
tok = lex();
unlex( tok );
// return type
if ( tok.token == TOKEN_ID ) {
auto tident = typeidentifier();
sig.add_child( tident );
} else {
ASTNode inserted_void( AST_TYPEID, -1, "$void" );
sig.add_child( inserted_void );
}
result.add_child( sig );
check_for_bad_semicolon();
// FunctionBody
auto blk = Block();
result.add_child( blk );
return result;
}
ASTNode TopLevelDecl() {
auto tok = lex();
unlex( tok );
ASTNode result;
switch ( tok.token ) {
case TOKEN_FUNC:
result = FunctionDecl();
break;
case TOKEN_VAR:
result = VarDecl();
result.type = AST_GLOBVAR;
break;
default:
error( tok.linenum, "top level declarations must begin with 'func' or 'var'" );
}
return result;
}
// SourceFile
ASTNode parse() {
ASTNode root( AST_PROGRAM );
Tokinfo tok;
while ( ( tok = lex() ).token != TOKEN_EOF ) {
unlex( tok );
auto decl = TopLevelDecl();
root.add_child( decl );
expect( TOKEN_SEMICOLON );
}
unlex( tok );
return root;
}