nomsu/core/errors.nom

#!/usr/bin/env nomsu -V4.8.10
#
    This file contains basic error reporting code

use "core/metaprogramming.nom"

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(barf %msg) compiles to "error(\(=lua "\%msg and \(%msg as lua expr) or 'nil'"), 0);"

(assume %condition) compiles to:
    lua> "\
        ..local \%assumption = 'Assumption failed: '..tostring((\%condition):get_source_code())"
    return (..)
        Lua "\
            ..if not \(%condition as lua expr) then
                error(\(quote "\%assumption"), 0)
            end"

(assume %a == %b) compiles to:
    lua> "\
        ..local \%assumption = 'Assumption failed: '..tostring(\(\(%a == %b) as nomsu))"
    define mangler
    return (..)
        Lua "\
            ..do
                local \(mangle "a"), \(mangle "b") = \(%a as lua expr), \(%b as lua expr)
                if \(mangle "a") ~= \(mangle "b") then
                    error(\(quote "\%assumption").."\\n"..tostring(\(mangle "a")).." != "..tostring(\(..)
                mangle "b"
            ..), 0)
                end
            end"

(assume %condition or barf %message) compiles to "\
    ..if not \(%condition as lua expr) then
        error(\(%message as lua expr), 0)
    end"

test:
    try (barf) and if it succeeds: barf "try failed."
    %worked = (no)
    try (barf) and if it barfs: %worked = (yes)
    assume %worked or barf "try/catch failed"
    %x = 1
    try:
        %x = 2
        do (barf) then always: %x = 3
    ..and if it barfs: do nothing
    
    assume (%x == 3) or barf "do/then always failed"

# Try/except
[..]
    try %action and if it succeeds %success or if it barfs %msg %fallback
    try %action and if it barfs %msg %fallback or if it succeeds %success
..all compile to "\
    ..do
        local fell_through = false
        local err, erred = nil, false
        local ok, ret = xpcall(function()
            \(%action as lua)
            fell_through = true
        end, function(\(=lua "\%fallback and \(%msg as lua expr) or ''"))
            local ok, ret = pcall(function()
                \((=lua "\%fallback or \%msg") as lua)
            end)
            if not ok then err, erred = ret, true end
        end)
        if ok then
            \(%success as lua)
            if not fell_through then
                return ret
            end
        elseif erred then
            error(err, 0)
        end
    end"

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#
    [..]
        try %action and if it succeeds %success or if it barfs %fallback
        try %action and if it barfs %fallback or if it succeeds %success
    ..all parse as (..)
        try %action and if it succeeds %success or if it barfs (=lua "") %fallback

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(try %action) parses as (..)
    try %action and if it succeeds (do nothing) or if it barfs (do nothing)

#(try %action and if it barfs %fallback) parses as (..)
    try %action and if it succeeds (do nothing) or if it barfs %fallback

(try %action and if it barfs %msg %fallback) parses as (..)
    try %action and if it succeeds (do nothing) or if it barfs %msg %fallback

(try %action and if it succeeds %success) parses as (..)
    try %action and if it succeeds %success or if it barfs (do nothing)