Initial commit

1 files changed, 74 insertions, 0 deletions

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+--- lam.read
+
+local read = {}
+
+local types = require "types"
+local util = require "util"
+
+function read.tokenize (str)
+        --[[ Convert a string of characters into a list of tokens ]]
+        assert(str, "No program given")
+        local tbl = {}
+        local word = ""
+        local push_word =
+                function ()
+                        if word:len() > 0 then
+                                table.insert(tbl, word)
+                                word = ""
+                        end
+                end
+
+        for c = 1, #str do
+                char = string.char(str:byte(c))
+                if char == " " or char == "\t" or char == "\n" then
+                        push_word()
+                elseif char == "(" then
+                        push_word()
+                        table.insert(tbl, "(")
+                elseif char == ")" then
+                        push_word()
+                        table.insert(tbl, ")")
+                else
+                        word = word .. char
+                end
+        end
+        push_word()
+        return tbl
+end
+
+function read.read (str)
+        -- [[ Read a scheme expression from a string ]]
+
+        local function Atom (token)
+                local n = tonumber(token)
+                if n then return n
+                else return tostring(token)
+                end
+        end
+
+        local function read_tokens (tokens)
+                --[[ Read a list of tokens from `tokenize' ]]
+                assert(next(tokens), "Unexpected EOF")
+                token = util.pop(tokens)
+                if token == "(" then
+                        local L = {}
+                        while tokens[1] ~= ")" do
+                                table.insert(L, read_tokens(tokens))
+                        end
+                        util.pop(tokens)                       --  remove ")"
+                        return L
+                elseif token == ")" then
+                        error("Unexpected ')'")
+                else
+                        return Atom(token)
+                end
+        end
+
+        return read_tokens(read.tokenize(str))
+end
+
+return setmetatable(read, { __call =
+                                    function(_, str)
+                                            return read.read(str)
+                                    end,
+})