Added shortness info-gathering to analyze_structure

analyze_structure.lua

@@ -24,6 +24,14 @@ local RESERVED_LUA_WORDS = {
     ['goto']     = true,
 }
 
+local SIMPLE_VALUE_TYPES = {
+    ['nil']      = true,
+    ['boolean']  = true,
+    ['number']   = true,
+}
+
+local SHORT_STRING_MAX_LEN = 7
+
 --------------------------------------------------------------------------------
 
 local function is_identifier(str)
@@ -131,6 +139,34 @@ local function is_tabular (t)
     return true
 end
 
+local is_short_table, is_simple_value
+
+function is_short_table (value)
+    -- Predicate: value is either an empty table, or one with a single simple
+    -- non-function element.
+
+    assert( type(value) == 'table', '[analyze_structure]: Only tables allowed!' )
+
+    local first_key   = next(value, nil)
+    if not first_key then
+        return true
+    elseif not next(value, first_key) == nil then
+        return false
+    end
+
+    return type(value[first_key]) ~= 'table'
+       and is_simple_value( value[first_key] )
+end
+
+function is_simple_value (value)
+    -- Predicate: value is either nil, a boolean, a number, a short string or a
+    -- short table.
+
+    return SIMPLE_VALUE_TYPES[ type(value) ]
+        or type(value) == 'string' and #value <= SHORT_STRING_MAX_LEN
+        or type(value) == 'table' and is_short_table(value)
+end
+
 --------------------------------------------------------------------------------
 
 local function get_table_info (t)
@@ -141,6 +177,7 @@ local function get_table_info (t)
 	      info.has_map     = key_types.nr_types > (key_types.number and 1 or 0)
           info.is_set      = is_set(t)
           info.is_tabular  = is_tabular(t)
+          info.is_short    = is_short_table(t)
 
     -- Determine type of table
 	if not info.has_seq and not info.has_map  then  info.type = 'empty'

test/test_analyze_structure.lua

@@ -84,6 +84,48 @@ SUITE:addTest('Not Tabular, due to varying lengths', function ()
     assert(table_info.is_tabular == false)
 end)
 
+SUITE:addTest('Very short/empty table', function ()
+    local input      = {  }
+    local table_info = analyze_structure(input)[input]
+
+    assert(table_info.is_short == true)
+end)
+
+SUITE:addTest('Very short table', function ()
+    local input      = { 1 }
+    local table_info = analyze_structure(input)[input]
+
+    assert(table_info.is_short == true)
+end)
+
+SUITE:addTest('Recursive tables are not simple', function ()
+    local input      = { {} }
+    local table_info = analyze_structure(input)[input]
+
+    assert(table_info.is_short == false)
+end)
+
+SUITE:addTest('Short strings are simple', function ()
+    local input      = { 'hello' }
+    local table_info = analyze_structure(input)[input]
+
+    assert(table_info.is_short == true)
+end)
+
+SUITE:addTest('Long strings are not', function ()
+    local input      = { 'hello world' }
+    local table_info = analyze_structure(input)[input]
+
+    assert(table_info.is_short == false)
+end)
+
+SUITE:addTest('Even maps can be simple!', function ()
+    local input      = { a = 4 }
+    local table_info = analyze_structure(input)[input]
+
+    assert(table_info.is_short == true)
+end)
+
 --------------------------------------------------------------------------------
 -- Corner cases.