How can I tell if a function call is an expression or a statement while writing a parser for a Lua-like language

Question

I'm trying to write a parser for a Lua-like language, using lex and yacc. It is a language without a forced statement terminator(a semicolon), and this feature made me not able to tell if a function call is a statement or a an expression.
For example, the following function:

function foo()  
  return { x = 5 }  
end

will return a table. Here are some usages:

foo()  -- this is a statement
t = foo()  -- foo is an expression
a = foo().x  -- foo() is a prefix-expression
print(foo())  -- foo() is an expression

I cannot write a no-conflict yacc code, because a simple function call could be an expression, a prefix-expression, or a statement.
How can I implement this feature? Is introducing forced statement terminators the only way?

Thank you very much.

You could have a look at the EBNF Lua grammar: lua.org/manual/5.1/manual.html#8 to see how they implemented things. — Bart Kiers
from what i see the simple function call would be part of the expressions/statements. You just have to reorder your grammar.(this makes it ugly to look at but parseable with yacc) — josefx

Lucero Lucero · Accepted Answer · 2010-11-12T11:53:25

I had a similar task to solve when implementing a T-SQL parser. I ended up including the ; as if it was mandatory in the grammar, and on syntax errors I would insert a virtual ; token to terminate the current statement and then have the parser retry the reduction.

For my use case this does work very well, maybe it could also work for yours.

How can I tell if a function call is an expression or a statement while writing a parser for a Lua-like language

1 Answers