458 lines
17 KiB
Plaintext
458 lines
17 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 "lib/metaprogramming.nom"
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use "lib/text.nom"
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use "lib/operators.nom"
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# No-Op
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immediately
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compile [do nothing] to code ""
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# Return
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immediately
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compile [return] to code "do return; end"
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compile [return %return_value] to code "do return \(%return_value as lua); end"
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# Conditionals
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immediately
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compile [if %condition %if_body] to code ".."
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if \(%condition as lua) then
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\(%if_body as lua statements)
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end --end if
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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 code ".."
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if \(%condition as lua) 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 --end if
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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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immediately
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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: (%when_true_expr's "type") in {Text:yes, List:yes, Dict:yes, Number:yes}
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return "(\(%condition as lua) and \(%when_true_expr as lua) or \(%when_false_expr as lua))"
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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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(function()
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if \(%condition as lua) then
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return \(%when_true_expr as lua);
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else
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return \(%when_false_expr as lua);
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end
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end)()
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# GOTOs
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immediately
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compile [=== %label ===, --- %label ---] to code ".."
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::label_\(nomsu "var_to_lua_identifier" [%label])::;
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compile [go to %label] to code ".."
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goto label_\(nomsu "var_to_lua_identifier" [%label]);
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# Basic loop control
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immediately
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compile [do next] to code "continue;"
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compile [stop] to code "break;"
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# Helper function
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immediately
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compile [for subtree %subtree where %condition in %tree %body] to code ".."
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for \(%subtree as lua) in coroutine.wrap(function() nomsu:walk_tree(\(%tree as lua)) end) do
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if type(\(%subtree as lua)) == 'table' and \(%subtree as lua).type then
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if \(%condition as lua) then
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\(%body as lua statements)
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end
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end
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end
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# While loops
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immediately
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compile [do next repetition] to code "goto continue_repeat;"
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compile [stop repeating] to code "goto stop_repeat;"
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compile [repeat while %condition %body] to code
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%continue_labels <- ""
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for subtree % where
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((%'s "type") = "FunctionCall") and ((%'s "stub") == "do next repetition")
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..in %body
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%continue_labels <- "\n::continue_repeat::;"
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stop
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%code <- ".."
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while \(%condition as lua) do
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\(%body as lua statements)\
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..\%continue_labels
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end --while-loop
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for subtree % where
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((%'s "type") = "FunctionCall") and ((%'s "stub") == "stop repeating")
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..in %body
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%code <- ".."
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do -- scope of "stop repeating" label
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\%code
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::stop_repeat::;
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end -- end of "stop repeating" label scope
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%continue_labels <- "\n::continue_repeat::;"
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stop
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return %code
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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 code
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%continue_labels <- ""
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for subtree % where
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((%'s "type") = "FunctionCall") and ((%'s "stub") == "do next repetition")
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..in %body
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%continue_labels <- "\n::continue_repeat::;"
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stop
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# This trashes the loop variables, just like in Python.
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%code <- ".."
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for i=1,\(%n as lua) do
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\(%body as lua statements)\
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..\%continue_labels
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end --numeric for-loop
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%stop_labels <- ""
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for subtree % where
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((%'s "type") = "FunctionCall") and ((%'s "stub") == "stop repeating")
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..in %body
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%code <- ".."
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do -- scope of "stop repeating" label
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\%code
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::stop_repeat::;
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end -- end of "stop repeating" label scope
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%continue_labels <- "\n::continue_repeat::;"
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stop
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return %code
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# For loop control flow:
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immediately
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compile [stop %var] to code ".."
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goto stop_\(nomsu "var_to_lua_identifier" [%var]);
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compile [do next %var] to code ".."
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goto continue_\(nomsu "var_to_lua_identifier" [%var]);
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# Numeric range for loops
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immediately
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compile [..]
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for %var from %start to %stop by %step %body
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for %var from %start to %stop via %step %body
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..to code
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%continue_labels <- ""
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for subtree % where
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((%'s "type") = "FunctionCall") and
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((%'s "stub") == "do next %") and
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((3rd in (%'s "value"))'s "src") == (%var's "src")
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..in %body
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%continue_labels <- "\n::continue_\(nomsu "var_to_lua_identifier" [%var])::;"
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stop
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if: (%var's "type") is "Var"
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%loop_var <- (%var as lua)
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%loop_var_shim <- ""
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..else
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%loop_var <- "i"
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%loop_var_shim <- "\n\(%var as lua) = i;"
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# This trashes the loop variables, just like in Python.
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%code <- ".."
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for \(%loop_var)=\(%start as lua),\(%stop as lua),\(%step as lua) do\
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..\%loop_var_shim
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\(%body as lua statements)\
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..\%continue_labels
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end --numeric for-loop
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for subtree % where
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((%'s "type") = "FunctionCall") and
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((%'s "stub") == "stop %") and
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((2nd in (%'s "value"))'s "src") == (%var's "src")
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..in %body
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%code <- ".."
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do -- scope for stopping for-loop
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\%code
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::stop_\(nomsu "var_to_lua_identifier" [%var])::;
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end -- end of scope for stopping for-loop
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stop
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return %code
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immediately
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parse [for %var from %start to %stop %body] as: for %var from %start to %stop via 1 %body
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parse [..]
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for all %start to %stop by %step %body
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for all %start to %stop via %step %body
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..as: for % from %start to %stop via %step %body
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parse [for all %start to %stop %body] as: for all %start to %stop via 1 %body
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# For-each loop
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immediately
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compile [for %var in %iterable %body] to code
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%continue_labels <- ""
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for subtree % where
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((%'s "type") = "FunctionCall") and
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((%'s "stub") == "do next %") and
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((3rd in (%'s "value"))'s "src") == (%var's "src")
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..in %body
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%continue_labels <- "\n::continue_\(nomsu "var_to_lua_identifier" [%var])::;"
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stop
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if: (%var's "type") is "Var"
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%loop_var <- (%var as lua)
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%loop_var_shim <- ""
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..else
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%loop_var <- "value"
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%loop_var_shim <- "\n\(%var as lua) = value;"
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# This trashes the loop variables, just like in Python.
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%code <- ".."
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for i,\%loop_var in ipairs(\(%iterable as lua)) do\
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..\%loop_var_shim
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\(%body as lua statements)\
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..\%continue_labels
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end --foreach-loop
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for subtree % where
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((%'s "type") = "FunctionCall") and
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((%'s "stub") == "stop %") and
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((2nd in (%'s "value"))'s "src") == (%var's "src")
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..in %body
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%code <- ".."
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do -- scope for stopping for-loop
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\%code
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::stop_\(nomsu "var_to_lua_identifier" [%var])::;
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end -- end of scope for stopping for-loop
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stop
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return %code
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parse [for all %iterable %body] as: for % in %iterable %body
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# Dict iteration (lua's "pairs()")
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immediately
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compile [for %key = %value in %iterable %body] to code
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%continue_labels <- ""
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for subtree % where
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((%'s "type") = "FunctionCall") and
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((%'s "stub") == "do next %") and
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((3rd in (%'s "value"))'s "src") == (%key's "src")
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..in %body
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<- %continue_labels + "\n::continue_\(nomsu "var_to_lua_identifier" [%key])::;"
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stop
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for subtree % where
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((%'s "type") = "FunctionCall") and
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((%'s "stub") == "do next %") and
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((3rd in (%'s "value"))'s "src") == (%value's "src")
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..in %body
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<- %continue_labels + "\n::continue_\(nomsu "var_to_lua_identifier" [%value])::;"
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stop
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if: (%key's "type") is "Var"
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%key_loop_var <- (%key as lua)
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%key_loop_var_shim <- ""
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..else
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%key_loop_var <- "key"
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%key_loop_var_shim <- "\n\(%key as lua) = key;"
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if: (%value's "type") is "Var"
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%value_loop_var <- (%value as lua)
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%value_loop_var_shim <- ""
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..else
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%value_loop_var <- "value"
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%value_loop_var_shim <- "\n\(%value as lua) = value;"
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# This trashes the loop variables, just like in Python.
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%code <- ".."
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for \%key_loop_var,\%value_loop_var in pairs(\(%iterable as lua)) do\
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..\%key_loop_var_shim\%value_loop_var_shim
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\(%body as lua statements)\
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..\%continue_labels
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end --foreach-loop
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%stop_labels <- ""
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for subtree % where
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((%'s "type") = "FunctionCall") and
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((%'s "stub") == "stop %") and
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((2nd in (%'s "value"))'s "src") == (%key's "src")
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..in %body
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<- %stop_labels + "\n::stop_\(nomsu "var_to_lua_identifier" [%key])::;"
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stop
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for subtree % where
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((%'s "type") = "FunctionCall") and
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((%'s "stub") == "stop %") and
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((2nd in (%'s "value"))'s "src") == (%value's "src")
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..in %body
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<- %stop_labels + "\n::stop_\(nomsu "var_to_lua_identifier" [%value])::;"
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stop
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if: %stop_labels is not ""
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%code <- ".."
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do -- scope for stopping for % = % loop
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\%code\%stop_labels
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end
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return %code
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# Switch statement/multi-branch if
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immediately
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compile [when %body] to code
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%result <- ""
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%fallthroughs <- []
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%is_first <- (yes)
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for %func_call in (%body's "value")
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assume ((%func_call's "type") is "FunctionCall") or barf ".."
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Invalid format for 'when' statement. Only '*' blocks are allowed.
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with [..]
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%tokens <- (%func_call's "value")
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%star <- (1st in %tokens)
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%condition <- (2nd in %tokens)
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%action <- (3rd in %tokens)
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..
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assume (=lua "\%star and \%star.type == 'Word' and \%star.value == '*'") 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 do> "table.insert(\%fallthroughs, \%condition)"
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do next %func_call
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if: =lua "\%condition.type == 'Word' and \%condition.value == 'else'"
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<- %result + ".."
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else
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\(%action as lua statements)
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stop
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..else
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%condition <- (%condition as lua)
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for all %fallthroughs
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<- %condition + " or \(% as lua)"
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<- %result + ".."
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\("if" if %is_first else "elseif") \%condition then
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\(%action as lua statements)
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%fallthroughs <- []
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%is_first <- (no)
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if: %result is not ""
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<- %result + "\nend"
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return %result
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# Switch statement
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immediately
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compile [when %branch_value = ? %body, when %branch_value is ? %body] to code
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%result <- ""
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%fallthroughs <- []
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%is_first <- (yes)
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%seen_else <- (no)
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for %func_call in (%body's "value")
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assume ((%func_call's "type") is "FunctionCall") or barf ".."
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Invalid format for 'when' statement. Only '*' blocks are allowed.
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%tokens <- (%func_call's "value")
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with [%star<-(1st in %tokens), %condition<-(2nd in %tokens), %action<-(3rd in %tokens)]
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assume (=lua "\%star and \%star.type == 'Word' and \%star.value == '*'") 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)"
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do next %func_call
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if: =lua "\%condition.type == 'Word' and \%condition.value == 'else'"
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assume (not %is_first) or barf "'else' clause cannot be first in 'when % = ?' block"
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<- %result + ".."
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else
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\(%action as lua statements)
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end
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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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%clause <- ""
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if: ((%condition's "type") is "Text") or ((%condition's "type") is "Number")
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%clause <- "branch_value == (\(%condition as lua))"
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..else
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%clause <- "utils.equivalent(branch_value, \(%condition as lua))"
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for all %fallthroughs
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if: ((%'s "type") is "Text") or ((%'s "type") is "Number")
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<- %clause + " or branch_value == (\(%condition as lua))"
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..else
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<- %clause + " or utils.equivalent(branch_value, \(%condition as lua))"
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<- %result + ".."
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\("if" if %is_first else "elseif") \%clause then
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\(%action as lua statements)
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%fallthroughs <- []
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%is_first <- (no)
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assume (%result is not "") or barf "No body for 'when % = ?' block!"
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unless %seen_else
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<- %result + "\nend"
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%result <- ".."
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do --when % = ?
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local branch_value = \(%branch_value as lua);\
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..\%result
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end --when % = ?
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return %result
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# Try/except
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immediately
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compile [..]
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try %action and if it succeeds %success or if it fails %fallback
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try %action and if it fails %fallback or if it succeeds %success
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..to code ".."
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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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if ok then
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\(%success as lua statements)
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end
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if not ok then
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\(%fallback as lua statements)
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elseif not fell_through then
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return ret;
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end
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end
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parse [try %action] as
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try %action and if it succeeds: do nothing
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..or if it fails: do nothing
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parse [try %action and if it fails %fallback] as
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try %action and if it succeeds: do nothing
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..or if it fails %fallback
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parse [try %action and if it succeeds %success] as
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try %action and if it succeeds %success or if it fails: do nothing
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# Do/finally:
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immediately
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compile [do %action] to code
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"do\n \(%action as lua statements)\nend" if ((%action's "type") is "Block")
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..else "(\(%action as lua))(nomsu);"
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compile [do %action then always %final_action] to code ".."
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do
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local fell_through = false;
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local ok, ret1 = 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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local ok2, ret2 = pcall(function()
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\(%final_action as lua statements)
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end);
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if not ok then error(ret1); end
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if not ok2 then error(ret2); end
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if not fell_through then
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return ret1;
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end
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end
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