local expr_lexer = require 'expr-lexer' local format, concat = string.format, table.concat local oper_table = expr_lexer.operators local ex_print local function is_ident_simple(s) return s:match('^[%l%u_][%w_]*$') end local function op_print(e, prio) if #e == 1 then local c, c_prio = ex_print(e[1]) if c_prio < prio then c = format('(%s)', c) end return format("%s%s", e.operator, c) else local a, a_prio = ex_print(e[1]) local b, b_prio = ex_print(e[2]) if a_prio < prio then a = format('(%s)', a) end if b_prio < prio then b = format('(%s)', b) end local temp = (prio < 2 and "%s %s %s" or "%s%s%s") return format(temp, a, e.operator, b) end end local function exlist_print(e) local t = {} for k = 1, #e do t[k] = ex_print(e[k]) end return concat(t, ', ') end ex_print = function(e) if type(e) == 'number' then return e, 3 elseif type(e) == 'string' then local s = e if not is_ident_simple(s) then s = format('[%s]', s) end return s, 3 elseif e.func then local arg_str = ex_print(e.arg) return format('%s(%s)', e.func, arg_str), 3 else local prio = oper_table[e.operator] local s = op_print(e, prio) return s, prio end end local function schema_print(e) local ys = exlist_print(e.y) local xs = exlist_print(e.x) local cs = exlist_print(e.conds) return format("%s ~ %s : %s", ys, xs, cs) end local function eval_operator(op, a, b) if op == '+' then return a + b elseif op == '-' then return a - b elseif op == '*' then return a * b elseif op == '/' then return a / b elseif op == '^' then return a ^ b elseif op == '=' then return (a == b and 1 or 0) elseif op == '>' then return (a> b and 1 or 0) elseif op == '<' then return (a < b and 1 or 0) else error('unkown operation: ' .. op) end end local function eval(expr, scope, scope_state) if type(expr) == 'number' then return expr elseif type(expr) == 'string' then return scope.ident(expr, scope_state) elseif expr.func then local arg_value = eval(expr.arg, scope, scope_state) if arg_value then local f = scope.func(expr) if not f then error('unknown function: ' .. expr.func) end return f(arg_value) end else if #expr == 1 then local v = eval(expr[1], scope, scope_state) if v then return -v end else local a = eval(expr[1], scope, scope_state) local b = eval(expr[2], scope, scope_state) if a and b then return eval_operator(expr.operator, a, b) end end end end -- return a set with all the variables referenced in a given expression local function ref_list_rec(expr, list) if type(expr) == 'number' then return elseif type(expr) == 'string' then list[expr] = true elseif expr.func then ref_list_rec(expr.arg, list) else if #expr == 1 then ref_list_rec(expr[1], list) else ref_list_rec(expr[1], list) ref_list_rec(expr[2], list) end end end return {schema = schema_print, expr = ex_print, expr_list = exlist_print, eval = eval, references = ref_list_rec}