I am now trying to understand how to do the CST->AST transformations for my
grammer. I was starting with just trying to transform the expression section
of my grammar (trying to follow the sample in
http://nat.truemesh.com/archives/000531.html)
I have a CST section that looks like:
expression {-> expression} =
{plus} [left]:expression plus [right]:term {->New
expression.add(left.expression,right.expression)}
| {minus} [left]:expression minus [right]:term {->New
expression.subtract(left.expression,right.expression)}
| {mod} [left]:expression modulo [right]:term {->New
expression.modulo(left.expression,right.expression)}
| {term} term {->term.expression}
;
term {-> expression} =
{mult} [left]:term star [right]:expon {->New
expression.multiply(left.expression,right.expression)}
| {div} [left]:term slash [right]:expon {->New
expression.divide(left.expression,right.expression)}
| {expon} expon {-> expon.expression}
;
expon {-> expression} =
{expon} [left]:expon power [right]:factor {->New
expression.power(left.expression,right.expression)}
| {factor} factor {-> factor.expression}
;
factor {-> expression } =
{unary} number {-> number.expression}
| {expression} l_par expression r_par {->
expression.expression}
;
number {->expression} =
{float} unop? [literal]:floating_point_literal {->New
expression.unary(unop.expression,literal)}
;
unop {-> expression} = {plus} plus
| {minus} minus // negate
;
and my AST section looks like:
Abstract Syntax Tree
expression = {add} [left]:expression [right]:expression
| {subtract} [left]:expression [right]:expression
| {multiply} [left]:expression [right]:expression
| {divide} [left]:expression [right]:expression
| {power} [left]:expression [right]:expression
| {modulo} [left]:expression [right]:expression
| {unary} unop? expression
;
unop =
{plus} plus
| {minus} minus // negate
;
The problem is that when I run this I get the following error from SableCC:
Verifying production transform identifiers.
Verifying ast alternatives transform identifiers.
java.lang.RuntimeException: [576,82] expecting #PUnop?# when #PExpression?# was
found
at org.sablecc.sablecc.ResolveTransformIds.error10(Unknown Source)
at org.sablecc.sablecc.ResolveTransformIds.checkTypeCompability(Unknown
Source)
at org.sablecc.sablecc.ResolveTransformIds.outANewTerm(Unknown Source)
I must have specified something incorrectly, but not sure what. It feels like
I should not have needed to put the "unop" section in the AST, but I couldn't
figure out how not to do that (SableCC would tell me that PUnop was undefined,
etc. if I didn't)
Thanks!
Roger
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