oak 0.8.0

A typed parser generator syntax extension for Parsing Expression Grammar (PEG).
Documentation 
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// Copyright 2016 Pierre Talbot (IRCAM)

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at

//     http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use back::compiler::*;

pub struct ChoiceCompiler
{
  choices: Vec<usize>,
  compiler: ExprCompilerFn
}

impl ChoiceCompiler
{
  pub fn recognizer(choices: Vec<usize>) -> ChoiceCompiler {
    ChoiceCompiler {
      choices: choices,
      compiler: recognizer_compiler
    }
  }

  pub fn parser(choices: Vec<usize>) -> ChoiceCompiler {
    ChoiceCompiler {
      choices: choices,
      compiler: parser_compiler
    }
  }
}

impl CompileExpr for ChoiceCompiler
{
  fn compile_expr<'a>(&self,  context: &mut Context<'a>,
    mut continuation: Continuation) -> syn::Expr
  {
    // Since we copy the success continuation for each branch, to avoid code explosion, we can extract it into a closure shared by all branches under criterion maintained by the context.
    continuation = context.success_as_closure(continuation);

    let mark = context.next_mark_name();
    let branch_failed = context.next_branch_failed_name();
    context.push_mut_ref_fv(branch_failed.clone(), parse_quote!(bool));

    // Each branch of the choice must be compiled in the same variable names environment (they share names of the variables they are building) and with a fresh success continuation size (each branch might create independent success continuation).
    let scope = context.save_scope();

    let mut choices = self.choices.clone();
    let last = choices.pop().unwrap();
    let mut branches: Vec<_> = choices.into_iter()
      .map(|idx| {
        context.restore_scope(scope.clone());
        let b = branch_failed.clone();
        let success: syn::Stmt = parse_quote!(#b = false;);
        continuation.compile_and_wrap(context, self.compiler, idx, success)
      })
      .collect();

    // The last branch does not need to assign `false` to the variable `branch_failed`.
    context.restore_scope(scope.clone());
    context.pop_mut_ref_fv();
    let (success, failure) = continuation.unwrap();
    branches.push(context.compile(self.compiler, last, success, failure));

    let mut branches_iter = branches.into_iter();
    let first = branches_iter.next().unwrap();

    let choice = branches_iter
      .rev()
      .fold(parse_quote!(state), |accu: syn::Expr, branch|
        parse_quote!({
          if #branch_failed {
            let mut state = state.restore_from_failure(#mark.clone());
            let state = #branch;
            #accu
          }
          else { state }
        }));

    parse_quote!({
      let #mark = state.mark();
      let mut #branch_failed = true;
      let state = #first;
      #choice
    })
  }
}