381 lines
14 KiB
Plaintext
381 lines
14 KiB
Plaintext
#
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This file contains compile-time actions that define basic control flow structures
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like "if" statements and loops.
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use "core/metaprogramming.nom"
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use "core/text.nom"
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use "core/operators.nom"
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use "core/errors.nom"
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# No-Op
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compile [do nothing] to: Lua ""
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# Conditionals
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compile [if %condition %if_body] to
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Lua ".."
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if \(%condition as lua expr) then
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\(%if_body as lua statements)
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end
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parse [unless %condition %unless_body] as: if (not %condition) %unless_body
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compile [if %condition %if_body else %else_body, unless %condition %else_body else %if_body] to
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Lua ".."
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if \(%condition as lua expr) then
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\(%if_body as lua statements)
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else
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\(%else_body as lua statements)
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end
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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# Conditional expression (ternary operator)
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# Note: this uses a function instead of "(condition and if_expr or else_expr)"
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because that breaks if %if_expr is falsey, e.g. "x < 5 and false or 99"
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compile [..]
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%when_true_expr if %condition else %when_false_expr
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%when_true_expr if %condition otherwise %when_false_expr
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%when_false_expr unless %condition else %when_true_expr
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%when_false_expr unless %condition then %when_true_expr
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..to
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# If %when_true_expr is guaranteed to be truthy, we can use Lua's idiomatic
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equivalent of a conditional expression: (cond and if_true or if_false)
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if: {Text:yes, List:yes, Dict:yes, Number:yes}.(%when_true_expr.type)
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return
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Lua value ".."
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(\(%condition as lua expr) and \(%when_true_expr as lua expr) or \(%when_false_expr as lua expr))
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..else
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# Otherwise, need to do an anonymous inline function (yuck, too bad lua
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doesn't have a proper ternary operator!)
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To see why this is necessary consider: (random()<.5 and false or 99)
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return
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Lua value ".."
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((function()
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if \(%condition as lua expr) then
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return \(%when_true_expr as lua expr)
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else
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return \(%when_false_expr as lua expr)
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end
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end)())
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# GOTOs
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compile [=== %label ===, --- %label ---, *** %label ***] to
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Lua "::label_\(%label as lua identifier)::"
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compile [go to %label] to
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Lua "goto label_\(%label as lua identifier)"
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# Basic loop control
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compile [do next] to: Lua "continue"
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compile [stop] to: Lua "break"
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# Helper function
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#TODO: do "using % compile %" instead so it's actually a helper function
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compile [%tree has subtree %subtree where %condition] to
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Lua value ".."
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(function()
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for \(%subtree as lua expr) in coroutine.wrap(function() \(%tree as lua expr):map(coroutine.yield) end) do
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if \(%condition as lua expr) then
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return true
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end
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end
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return false
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end)()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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# While loops
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compile [do next repeat] to: Lua "goto continue_repeat"
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compile [stop repeating] to: Lua "goto stop_repeat"
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compile [repeat while %condition %body] to
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%lua <-
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Lua ".."
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while \(%condition as lua expr) do
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\(%body as lua statements)
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if
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%body has subtree % where: (%.type = "Action") and (%.stub is "do next repeat")
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..: to %lua write "\n ::continue_repeat::"
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to %lua write "\nend --while-loop"
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if
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%body has subtree % where: (%.type = "Action") and (%.stub is "stop repeating")
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..
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%lua <-
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Lua ".."
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do -- scope of "stop repeating" label
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\%lua
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::stop_repeat::
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end -- end of "stop repeating" label scope
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return %lua
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parse [repeat %body] as: repeat while (yes) %body
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parse [repeat until %condition %body] as: repeat while (not %condition) %body
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compile [..]
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repeat %n times %body
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..to
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%lua <-
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Lua ".."
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for i=1,\(%n as lua expr) do
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\(%body as lua statements)
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if
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%body has subtree % where: (%.type = "Action") and (%.stub is "do next repeat")
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..: to %lua write "\n ::continue_repeat::"
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to %lua write "\nend --numeric for-loop"
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if
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%body has subtree % where: (%.type = "Action") and (%.stub is "stop repeating")
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..
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%lua <-
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Lua ".."
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do -- scope of "stop repeating" label
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\%lua
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::stop_repeat::
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end -- end of "stop repeating" label scope
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return %lua
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# For loop control flow
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compile [stop %var] to
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Lua "goto stop_\(%var as lua identifier)"
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compile [do next %var] to
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Lua "goto continue_\(%var as lua identifier)"
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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# Numeric range for loops
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compile [..]
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for %var in %start to %stop by %step %body
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for %var in %start to %stop via %step %body
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..to
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# This uses Lua's approach of only allowing loop-scoped variables in a loop
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assume (%var.type is "Var") or barf "Loop expected variable, not: \%var"
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%lua <-
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Lua ".."
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for \(%var as lua expr)=\(%start as lua expr),\(%stop as lua expr),\(%step as lua expr) do
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\(%body as lua statements)
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if
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%body has subtree % where
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(%.type = "Action") and
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(%.stub is "do next %") and
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%.(3).1 = %var.1
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..: to %lua write "\n ::continue_\(%var as lua identifier)::"
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to %lua write "\nend --numeric for-loop"
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if
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%body has subtree % where
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(%.type = "Action") and
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(%.stub is "stop %") and
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%.(2).1 = %var.1
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..
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%lua <-
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Lua ".."
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do -- scope for stopping for-loop
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\%lua
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::stop_\(%var as lua identifier)::
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end -- end of scope for stopping for-loop
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return %lua
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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parse [for %var in %start to %stop %body] as: for %var in %start to %stop via 1 %body
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# For-each loop (lua's "ipairs()")
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compile [for %var in %iterable %body] to
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# This uses Lua's approach of only allowing loop-scoped variables in a loop
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assume (%var.type is "Var") or barf "Loop expected variable, not: \%var"
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%lua <-
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Lua ".."
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for i,\(%var as lua identifier) in ipairs(\(%iterable as lua expr)) do
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\(%body as lua statements)
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if
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%body has subtree % where
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(%.type = "Action") and
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(%.stub is "do next %") and
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%.3.(1) = %var.(1)
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..: to %lua write (Lua "\n::continue_\(%var as lua identifier)::")
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to %lua write "\nend --foreach-loop"
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if
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%body has subtree % where
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(%.type = "Action") and
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(%.stub is "stop %") and
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%.2.(1) = %var.(1)
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..
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%lua <-
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Lua ".."
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do -- scope for stopping for-loop
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\%lua
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::stop_\(%var as lua identifier)::
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end -- end of scope for stopping for-loop
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return %lua
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# Dict iteration (lua's "pairs()")
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compile [..]
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for %key = %value in %iterable %body
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for (%key,%value) in %iterable %body
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..to
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# This uses Lua's approach of only allowing loop-scoped variables in a loop
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assume (%key.type is "Var") or barf "Loop expected variable, not: \%key"
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assume (%value.type is "Var") or barf "Loop expected variable, not: \%value"
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%lua <-
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Lua ".."
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for \(%key as lua identifier),\(%value as lua identifier) in pairs(\(%iterable as lua expr)) do
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\(%body as lua statements)
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if
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%body has subtree % where
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(%.type = "Action") and
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(%.stub is "do next %") and
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%.3.(1) = %key.(1)
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..: to %lua write (Lua "\n::continue_\(%key as lua identifier)::")
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if
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%body has subtree % where
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(%.type = "Action") and
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(%.stub is "do next %") and
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%.3.(1) = %value.(1)
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..: to %lua write (Lua "\n::continue_\(%value as lua identifier)::")
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to %lua write "\nend --foreach-loop"
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%stop_labels <- (Lua "")
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if
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%body has subtree % where
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(%.type = "Action") and
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(%.stub is "stop %") and
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%.2.(1) = %key.(1)
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..: to %stop_labels write "\n::stop_\(%key as lua identifier)::"
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if
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%body has subtree % where
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(%.type = "Action") and
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(%.stub is "stop %") and
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%.2.(1) = %value.(1)
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..: to %stop_labels write "\n::stop_\(%value as lua identifier)::"
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if: (length of "\%stop_labels") > 0
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%lua <-
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Lua ".."
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do -- scope for stopping for % = % loop
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\%lua\%stop_labels
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end
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return %lua
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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# Switch statement/multi-branch if
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compile [when %body] to
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%code <- (Lua "")
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%fallthroughs <- []
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%is_first <- (yes)
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%seen_else <- (no)
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%branches <-
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%body if (%body.type = "Block") else [%body]
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for %func_call in %branches
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assume (%func_call.type is "Action") or barf ".."
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Invalid format for 'when' statement. Only '*' blocks are allowed.
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with {..}
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%star: %func_call.1
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%condition: %func_call.2
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%action: %func_call.3
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..
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assume (%star = "*") or barf ".."
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Invalid format for 'when' statement. Lines must begin with '*'
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assume %condition or barf ".."
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Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"
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if: %action is (nil)
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lua> "table.insert(\%fallthroughs, \(%condition as lua expr))"
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do next %func_call
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if: %condition = "else"
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assume (not %is_first) or barf "'else' clause cannot be first in 'when % = ?' block"
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to %code write "\nelse\n "
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to %code write: %action as lua statements
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%seen_else <- (yes)
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..else
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assume (not %seen_else) or barf "'else' clause needs to be last in 'when' block"
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lua> "table.insert(\%fallthroughs, \(%condition as lua expr))"
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to %code write "\("if" if %is_first else "\nelseif") "
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for %i = %condition in %fallthroughs
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if (%i > 1): to %code write " or "
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to %code write %condition
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to %code write " then\n "
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to %code write (%action as lua statements)
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%fallthroughs <- []
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%is_first <- (no)
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assume (%fallthroughs = []) or barf "Unfinished fallthrough conditions in 'when' block"
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assume ((length of "\%code") > 0) or barf "Empty body for 'when' block"
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to %code write "\nend --when"
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return %code
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# Switch statement
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compile [when %branch_value = ? %body, when %branch_value is ? %body] to
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%code <- (Lua "")
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%fallthroughs <- []
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%is_first <- (yes)
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%seen_else <- (no)
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%branches <-
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%body if (%body.type = "Block") else [%body]
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for %func_call in %branches
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assume (%func_call.type is "Action") or barf ".."
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Invalid format for 'when' statement. Only '*' blocks are allowed.
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with {%star:%func_call.1, %condition:%func_call.2, %action:%func_call.3}
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assume (%star = "*") or barf ".."
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Invalid format for 'when' statement. Lines must begin with '*'
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assume %condition or barf ".."
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Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"
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if: %action is (nil)
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lua> "table.insert(\%fallthroughs, \(%condition as lua expr))"
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do next %func_call
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if: %condition = "else"
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assume (not %is_first) or barf "'else' clause cannot be first in 'when % = ?' block"
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to %code write "\nelse\n "
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to %code write: %action as lua statements
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..else
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assume (not %seen_else) or barf "'else' clause needs to be last in 'when % = ?' block"
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to %code write "\("if" if %is_first else "\nelseif") "
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lua> "table.insert(\%fallthroughs, \(%condition as lua expr))"
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for %i = % in %fallthroughs
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if: %i > 1
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to %code write " or "
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if: (%.type is "Text") or (%.type is "Number")
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to %code write "branch_value == \%"
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..else
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to %code write "utils.equivalent(branch_value, \%)"
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to %code write "then\n "
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to %code write (%action as lua statements)
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%fallthroughs <- []
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%is_first <- (no)
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assume (%fallthroughs = []) or barf "Unfinished fallthrough conditions in 'when' block"
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assume ((length of "\%code") > 0) or barf "No body for 'when % = ?' block!"
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to %code write "\nend"
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%code <-
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Lua ".."
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do --when % = ?
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local branch_value = \(%branch_value as lua expr)
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\%code
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end --when % = ?
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return %code
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# Do/finally
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compile [do %action] to
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Lua ".."
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do
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\(%action as lua statements)
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end --do
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compile [do %action then always %final_action] to
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Lua ".."
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do
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local fell_through = false
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local ok, ret = pcall(function()
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\(%action as lua statements)
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fell_through = true
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end)
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\(%final_action as lua statements)
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if not ok then error(ret, 0) end
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if not fell_through then return ret end
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end
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# Inline thunk:
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compile [result of %body] to
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Lua value "(\(compile as: [] -> %body))()"
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