object SwitchC singleton

inherit: Construct

// MANIFEST

manifest get 
  return:
    'constructs':
      'switch':
        repeats false
        clauses:
          'switch': #exprout
          'case': #exprsblock
          'else': #block
        handler bind SwitchConstruct
      
      
docs get
  return !Documents
  
  

///////////////   SWITCH
//
//

SwitchConstruct task expects $clauses, $tools

  if ($clauses | last).clause isnt 'else'
    return: error "SAI Complier: Every SWITCH statement should have an ELSE clause at the end. (If it's in the middle of the CASES, move it to the end.)"

  with ($clauses | has .clause is 'else') | count
    if it > 1
      return: error "SAI Compiler: Found ${it} ELSE clauses in SWITCH; only one is required."
      
  set 
    body ''
    outs !@OutVarHelper $clauses.0.args.out
    trialvar fields 'trial' outs.0 or !$tools.addlocal 

  ply $clauses
  
    switch .type
    case 'switch.exprout'
      set
        vars to trialvar | update:
          'condition' .args.expr
          
        text '''
          switch (^{trial}=(^{condition})) {
          
        body + !$tools.replacer text, vars 
      
    case 'case.exprsblock'
      set
        cases to .args.exprs.2 | total 'case ${.}:\n'
          
        vars trialvar | update:
          'cases' cases
          'block' .args.block

        text '''
          ^{cases}
          ^{block}
          break;
          
        body + !$tools.replacer text, vars
        
    case 'else.block'
      set
        vars trialvar | update:
          'block' .args.block

        text '''
          default:
          ^{block}
          break;
          
        body + !$tools.replacer text, vars
              
    else
      return: error "Unhandled construct type ${.type} in SwitchConstruct"

  set body + '}'

  return: body body


Documents task
  return:
    'constructs':
      'switch':
        subtitle 'choice-based conditional'
        summary '''
          Choose among alternatives based on expression equality. 
        detail '''
          The expression under evaluation is available to all codepaths 
          as **trial** (which can be renamed with the **as** clause).

          Unlike the native Javascript `switch` these __case__ clauses do not fall through;
          the break is implicit.  (Though you can break out early.)

              switch ~System.IO.Keypress() as key
              case 'n', 'N'
                Move 0,-1
              case 's', 'S'
                Move 0,1
              case 'e', 'E'
                Move 1,0
              case 'w', 'W'
                Move -1,0
              case ' '
                Jump
              case '?'
                Help
              else
                Emit 'Key [$\{key}] isn't used; type ? for help.'

          The compiler will insist on an __else__ clause as a matter of good programming hygeine.