From 688d2230b93b03f2d4505346ef3b89b0f4c46445 Mon Sep 17 00:00:00 2001 From: Cliff Click Date: Mon, 11 Nov 2024 09:55:48 -0800 Subject: Allow C-style for loops --- .../main/java/com/seaofnodes/simple/Parser.java | 111 ++++++++++++++++++--- 1 file changed, 95 insertions(+), 16 deletions(-) (limited to 'chapter17/src/main/java') diff --git a/chapter17/src/main/java/com/seaofnodes/simple/Parser.java b/chapter17/src/main/java/com/seaofnodes/simple/Parser.java index 799e0629..a4f7462e 100644 --- a/chapter17/src/main/java/com/seaofnodes/simple/Parser.java +++ b/chapter17/src/main/java/com/seaofnodes/simple/Parser.java @@ -212,6 +212,7 @@ public class Parser { else if (match ("{") ) return require(parseBlock(false),"}"); else if (matchx("if") ) return parseIf(); else if (matchx("while") ) return parseWhile(); + else if (matchx("for") ) return parseFor(); else if (matchx("break") ) return parseBreak(); else if (matchx("continue")) return parseContinue(); else if (matchx("struct") ) return parseStruct(); @@ -221,6 +222,7 @@ public class Parser { // to ambiguity else return parseExpressionStatement(); } + /** * Parses a while statement * @@ -230,11 +232,40 @@ public class Parser { * @return a {@link Node}, never {@code null} */ private Node parseWhile() { + require("("); + return parseLooping(false); + } - var savedContinueScope = _continueScope; - var savedBreakScope = _breakScope; + /** + * Parses a for statement + * + * 
+     *     for( var x=init; test; incr ) body
+     *
+ * @return a {@link Node}, never {@code null} + */ + private Node parseFor() { + // { var x=init,y=init,...; + // while( pred ) { + // body; + // next; + // } + // } require("("); + _scope.push(); // Scope for the index variables + if( !match(";") ) // Can be empty init "for(;test;next) body" + parseExpressionStatement(); // Non-empty init + Node rez = parseLooping(true); + _scope.pop(); // Exit index variable scope + return rez; + } + + // Shared by `for` and `while` + private Node parseLooping( boolean doFor ) { + + var savedContinueScope = _continueScope; + var savedBreakScope = _breakScope; // Loop region has two control inputs, the first is the entry // point, and second is back edge that is set after loop is parsed @@ -255,13 +286,25 @@ public class Parser { _xScopes.push(_scope = _scope.dup(true)); // The true argument triggers creating phis // Parse predicate - var pred = require(parseExpression(), ")"); + var pred = peek(';') ? con(1) : parseExpression(); + require( doFor ? ";" : ")" ); + // IfNode takes current control and predicate - Node ifNode = new IfNode(ctrl(), pred).peephole(); + Node ifNode = new IfNode(ctrl(), pred.keep()).peephole(); // Setup projection nodes Node ifT = new CProjNode(ifNode. keep(), 0, "True" ).peephole().keep(); Node ifF = new CProjNode(ifNode.unkeep(), 1, "False").peephole(); + // for( ;;next ) body + int nextPos = -1, nextEnd = -1; + if( doFor ) { + // Skip the next expression and parse it later + nextPos = pos(); + skipAsgn(); + nextEnd = pos(); + require(")"); + } + // Clone the body Scope to create the break/exit Scope which accounts for any // side effects in the predicate. The break/exit Scope will be the final // scope after the loop, and its control input is the False branch of @@ -276,7 +319,7 @@ public class Parser { // Parse the true side, which corresponds to loop body // Our current scope is the body Scope ctrl(ifT.unkeep()); // set ctrl token to ifTrue projection - _scope.addGuards(ifT,pred,false); // Up-cast predicate + _scope.addGuards(ifT,pred.unkeep(),false); // Up-cast predicate parseStatement(); // Parse loop body _scope.removeGuards(ifT); @@ -287,6 +330,15 @@ public class Parser { _scope = _continueScope; } + // Now append the next code onto the body code + if( doFor ) { + int old = pos(nextPos); + if( !peek(')') ) + parseAsgn(null,false); + assert pos() == nextEnd; + pos(old); + } + // The true branch loops back, so whatever is current _scope.ctrl gets // added to head loop as input. endLoop() updates the head scope, and // goes through all the phis that were created earlier. For each phi, @@ -342,6 +394,26 @@ public class Parser { return _breakScope; } + // Look for an unbalanced `)`, skipping balanced + private void skipAsgn() { + int paren=0; + while( true ) + // Next X char handles skipping complex comments + switch( _lexer.nextXChar() ) { + case Character.MAX_VALUE: + throw Utils.TODO(); + case ')': + if( --paren<0 ) { + pos(pos()-1); // Leave the `)` behind + return; + } + break; + case '(': paren ++; break; + default: break; + } + } + + /** * Parses a statement * @@ -443,13 +515,13 @@ public class Parser { // t==type && expr ==>> declaratn: final=inCon && noBang, expr=parse() ; t:=type; private Node parseAsgn(Type t, boolean hasBang) { boolean isDecl = t!=null; - int old = _lexer._position; + int old = pos(); String name = requireId(); boolean hasType = t!=null && t!=Type.TOP && t!=Type.BOTTOM; // User written type boolean hasExpr = !(peek(';') || peek(',')); // Expression follows if( hasExpr && !match("=") ) // Something else - { _lexer._position = old; return null; } + { pos(old); return parseExpression(); } if( !hasExpr && t==Type.BOTTOM ) throw errorSyntax("expression"); Node expr = hasExpr ? parseExpression() : con(t.makeInit()); boolean xfinal = t==Type.TOP || (hasType && hasExpr && !hasBang && _scope.inCon()); @@ -523,10 +595,8 @@ public class Parser { n = parseFinal(t); // Parse "asgn;" which is just "name = expr;" - } else if( ( n = parseAsgn(null,false)) == null ) { - // Something else - n = parseExpression(); - } + } else + n = parseAsgn(null,false); return require(n,";"); } @@ -577,14 +647,14 @@ public class Parser { // types (which ARE valid here) from local vars in an (optional) forward // ref type position. private Type type() { - int old1 = _lexer._position; + int old1 = pos(); String tname = _lexer.matchId(); if( tname==null ) return null; // Convert the type name to a type. Type t0 = TYPES.get(tname); // No new types as keywords if( t0 == null && KEYWORDS.contains(tname) ) - { _lexer._position = old1; return null; } + { pos(old1); return null; } Type t1 = t0 == null ? TypeMemPtr.make(TypeStruct.makeFRef(tname)) : t0; // Null: assume a forward ref type // Nest arrays and '?' as needed while( true ) { @@ -607,11 +677,11 @@ public class Parser { if( t0 != null ) return t1; // Check valid forward ref, after parsing all the type extra bits. // Cannot check earlier, because cannot find required 'id' until after "[]?" syntax - int old2 = _lexer._position; + int old2 = pos(); String id = _lexer.matchId(); - _lexer._position = old2; // Reset lexer to reparse + pos(old2); // Reset lexer to reparse if( id==null ) { - _lexer._position = old1; // Reset lexer to reparse + pos(old1); // Reset lexer to reparse return null; // Not a type } // Yes a forward ref, so declare it @@ -1040,6 +1110,13 @@ public class Parser { private boolean peek(char ch) { return _lexer.peek(ch); } private boolean peekIsId() { return _lexer.peekIsId(); } + private int pos() { return _lexer._position; } + private int pos(int pos) { + int old = _lexer._position; + _lexer._position = pos; + return old; + } + // Require and return an identifier private String requireId() { String id = _lexer.matchId(); @@ -1134,6 +1211,8 @@ public class Parser { } } + // Next non-white-space character, or EOF + public char nextXChar() { skipWhiteSpace(); return nextChar(); } // Return true, if we find "syntax" after skipping white space; also // then advance the cursor past syntax. -- cgit v1.2.3