diff --git a/edify/expr.cpp b/edify/expr.cpp
new file mode 100644
index 0000000..cd1e087
--- /dev/null
+++ b/edify/expr.cpp
@@ -0,0 +1,507 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <string.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <unistd.h>
+
+#include "expr.h"
+
+// Functions should:
+//
+//    - return a malloc()'d string
+//    - if Evaluate() on any argument returns NULL, return NULL.
+
+int BooleanString(const char* s) {
+    return s[0] != '\0';
+}
+
+char* Evaluate(State* state, Expr* expr) {
+    Value* v = expr->fn(expr->name, state, expr->argc, expr->argv);
+    if (v == NULL) return NULL;
+    if (v->type != VAL_STRING) {
+        ErrorAbort(state, "expecting string, got value type %d", v->type);
+        FreeValue(v);
+        return NULL;
+    }
+    char* result = v->data;
+    free(v);
+    return result;
+}
+
+Value* EvaluateValue(State* state, Expr* expr) {
+    return expr->fn(expr->name, state, expr->argc, expr->argv);
+}
+
+Value* StringValue(char* str) {
+    if (str == NULL) return NULL;
+    Value* v = reinterpret_cast<Value*>(malloc(sizeof(Value)));
+    v->type = VAL_STRING;
+    v->size = strlen(str);
+    v->data = str;
+    return v;
+}
+
+void FreeValue(Value* v) {
+    if (v == NULL) return;
+    free(v->data);
+    free(v);
+}
+
+Value* ConcatFn(const char* name, State* state, int argc, Expr* argv[]) {
+    if (argc == 0) {
+        return StringValue(strdup(""));
+    }
+    char** strings = reinterpret_cast<char**>(malloc(argc * sizeof(char*)));
+    int i;
+    for (i = 0; i < argc; ++i) {
+        strings[i] = NULL;
+    }
+    char* result = NULL;
+    int length = 0;
+    for (i = 0; i < argc; ++i) {
+        strings[i] = Evaluate(state, argv[i]);
+        if (strings[i] == NULL) {
+            goto done;
+        }
+        length += strlen(strings[i]);
+    }
+
+    result = reinterpret_cast<char*>(malloc(length+1));
+    int p;
+    p = 0;
+    for (i = 0; i < argc; ++i) {
+        strcpy(result+p, strings[i]);
+        p += strlen(strings[i]);
+    }
+    result[p] = '\0';
+
+  done:
+    for (i = 0; i < argc; ++i) {
+        free(strings[i]);
+    }
+    free(strings);
+    return StringValue(result);
+}
+
+Value* IfElseFn(const char* name, State* state, int argc, Expr* argv[]) {
+    if (argc != 2 && argc != 3) {
+        free(state->errmsg);
+        state->errmsg = strdup("ifelse expects 2 or 3 arguments");
+        return NULL;
+    }
+    char* cond = Evaluate(state, argv[0]);
+    if (cond == NULL) {
+        return NULL;
+    }
+
+    if (BooleanString(cond) == true) {
+        free(cond);
+        return EvaluateValue(state, argv[1]);
+    } else {
+        if (argc == 3) {
+            free(cond);
+            return EvaluateValue(state, argv[2]);
+        } else {
+            return StringValue(cond);
+        }
+    }
+}
+
+Value* AbortFn(const char* name, State* state, int argc, Expr* argv[]) {
+    char* msg = NULL;
+    if (argc > 0) {
+        msg = Evaluate(state, argv[0]);
+    }
+    free(state->errmsg);
+    if (msg) {
+        state->errmsg = msg;
+    } else {
+        state->errmsg = strdup("called abort()");
+    }
+    return NULL;
+}
+
+Value* AssertFn(const char* name, State* state, int argc, Expr* argv[]) {
+    int i;
+    for (i = 0; i < argc; ++i) {
+        char* v = Evaluate(state, argv[i]);
+        if (v == NULL) {
+            return NULL;
+        }
+        int b = BooleanString(v);
+        free(v);
+        if (!b) {
+            int prefix_len;
+            int len = argv[i]->end - argv[i]->start;
+            char* err_src = reinterpret_cast<char*>(malloc(len + 20));
+            strcpy(err_src, "assert failed: ");
+            prefix_len = strlen(err_src);
+            memcpy(err_src + prefix_len, state->script + argv[i]->start, len);
+            err_src[prefix_len + len] = '\0';
+            free(state->errmsg);
+            state->errmsg = err_src;
+            return NULL;
+        }
+    }
+    return StringValue(strdup(""));
+}
+
+Value* SleepFn(const char* name, State* state, int argc, Expr* argv[]) {
+    char* val = Evaluate(state, argv[0]);
+    if (val == NULL) {
+        return NULL;
+    }
+    int v = strtol(val, NULL, 10);
+    sleep(v);
+    return StringValue(val);
+}
+
+Value* StdoutFn(const char* name, State* state, int argc, Expr* argv[]) {
+    int i;
+    for (i = 0; i < argc; ++i) {
+        char* v = Evaluate(state, argv[i]);
+        if (v == NULL) {
+            return NULL;
+        }
+        fputs(v, stdout);
+        free(v);
+    }
+    return StringValue(strdup(""));
+}
+
+Value* LogicalAndFn(const char* name, State* state,
+                   int argc, Expr* argv[]) {
+    char* left = Evaluate(state, argv[0]);
+    if (left == NULL) return NULL;
+    if (BooleanString(left) == true) {
+        free(left);
+        return EvaluateValue(state, argv[1]);
+    } else {
+        return StringValue(left);
+    }
+}
+
+Value* LogicalOrFn(const char* name, State* state,
+                   int argc, Expr* argv[]) {
+    char* left = Evaluate(state, argv[0]);
+    if (left == NULL) return NULL;
+    if (BooleanString(left) == false) {
+        free(left);
+        return EvaluateValue(state, argv[1]);
+    } else {
+        return StringValue(left);
+    }
+}
+
+Value* LogicalNotFn(const char* name, State* state,
+                    int argc, Expr* argv[]) {
+    char* val = Evaluate(state, argv[0]);
+    if (val == NULL) return NULL;
+    bool bv = BooleanString(val);
+    free(val);
+    return StringValue(strdup(bv ? "" : "t"));
+}
+
+Value* SubstringFn(const char* name, State* state,
+                   int argc, Expr* argv[]) {
+    char* needle = Evaluate(state, argv[0]);
+    if (needle == NULL) return NULL;
+    char* haystack = Evaluate(state, argv[1]);
+    if (haystack == NULL) {
+        free(needle);
+        return NULL;
+    }
+
+    char* result = strdup(strstr(haystack, needle) ? "t" : "");
+    free(needle);
+    free(haystack);
+    return StringValue(result);
+}
+
+Value* EqualityFn(const char* name, State* state, int argc, Expr* argv[]) {
+    char* left = Evaluate(state, argv[0]);
+    if (left == NULL) return NULL;
+    char* right = Evaluate(state, argv[1]);
+    if (right == NULL) {
+        free(left);
+        return NULL;
+    }
+
+    char* result = strdup(strcmp(left, right) == 0 ? "t" : "");
+    free(left);
+    free(right);
+    return StringValue(result);
+}
+
+Value* InequalityFn(const char* name, State* state, int argc, Expr* argv[]) {
+    char* left = Evaluate(state, argv[0]);
+    if (left == NULL) return NULL;
+    char* right = Evaluate(state, argv[1]);
+    if (right == NULL) {
+        free(left);
+        return NULL;
+    }
+
+    char* result = strdup(strcmp(left, right) != 0 ? "t" : "");
+    free(left);
+    free(right);
+    return StringValue(result);
+}
+
+Value* SequenceFn(const char* name, State* state, int argc, Expr* argv[]) {
+    Value* left = EvaluateValue(state, argv[0]);
+    if (left == NULL) return NULL;
+    FreeValue(left);
+    return EvaluateValue(state, argv[1]);
+}
+
+Value* LessThanIntFn(const char* name, State* state, int argc, Expr* argv[]) {
+    if (argc != 2) {
+        free(state->errmsg);
+        state->errmsg = strdup("less_than_int expects 2 arguments");
+        return NULL;
+    }
+
+    char* left;
+    char* right;
+    if (ReadArgs(state, argv, 2, &left, &right) < 0) return NULL;
+
+    bool result = false;
+    char* end;
+
+    long l_int = strtol(left, &end, 10);
+    if (left[0] == '\0' || *end != '\0') {
+        goto done;
+    }
+
+    long r_int;
+    r_int = strtol(right, &end, 10);
+    if (right[0] == '\0' || *end != '\0') {
+        goto done;
+    }
+
+    result = l_int < r_int;
+
+  done:
+    free(left);
+    free(right);
+    return StringValue(strdup(result ? "t" : ""));
+}
+
+Value* GreaterThanIntFn(const char* name, State* state,
+                        int argc, Expr* argv[]) {
+    if (argc != 2) {
+        free(state->errmsg);
+        state->errmsg = strdup("greater_than_int expects 2 arguments");
+        return NULL;
+    }
+
+    Expr* temp[2];
+    temp[0] = argv[1];
+    temp[1] = argv[0];
+
+    return LessThanIntFn(name, state, 2, temp);
+}
+
+Value* Literal(const char* name, State* state, int argc, Expr* argv[]) {
+    return StringValue(strdup(name));
+}
+
+Expr* Build(Function fn, YYLTYPE loc, int count, ...) {
+    va_list v;
+    va_start(v, count);
+    Expr* e = reinterpret_cast<Expr*>(malloc(sizeof(Expr)));
+    e->fn = fn;
+    e->name = "(operator)";
+    e->argc = count;
+    e->argv = reinterpret_cast<Expr**>(malloc(count * sizeof(Expr*)));
+    int i;
+    for (i = 0; i < count; ++i) {
+        e->argv[i] = va_arg(v, Expr*);
+    }
+    va_end(v);
+    e->start = loc.start;
+    e->end = loc.end;
+    return e;
+}
+
+// -----------------------------------------------------------------
+//   the function table
+// -----------------------------------------------------------------
+
+static int fn_entries = 0;
+static int fn_size = 0;
+NamedFunction* fn_table = NULL;
+
+void RegisterFunction(const char* name, Function fn) {
+    if (fn_entries >= fn_size) {
+        fn_size = fn_size*2 + 1;
+        fn_table = reinterpret_cast<NamedFunction*>(realloc(fn_table, fn_size * sizeof(NamedFunction)));
+    }
+    fn_table[fn_entries].name = name;
+    fn_table[fn_entries].fn = fn;
+    ++fn_entries;
+}
+
+static int fn_entry_compare(const void* a, const void* b) {
+    const char* na = ((const NamedFunction*)a)->name;
+    const char* nb = ((const NamedFunction*)b)->name;
+    return strcmp(na, nb);
+}
+
+void FinishRegistration() {
+    qsort(fn_table, fn_entries, sizeof(NamedFunction), fn_entry_compare);
+}
+
+Function FindFunction(const char* name) {
+    NamedFunction key;
+    key.name = name;
+    NamedFunction* nf = reinterpret_cast<NamedFunction*>(bsearch(&key, fn_table, fn_entries,
+            sizeof(NamedFunction), fn_entry_compare));
+    if (nf == NULL) {
+        return NULL;
+    }
+    return nf->fn;
+}
+
+void RegisterBuiltins() {
+    RegisterFunction("ifelse", IfElseFn);
+    RegisterFunction("abort", AbortFn);
+    RegisterFunction("assert", AssertFn);
+    RegisterFunction("concat", ConcatFn);
+    RegisterFunction("is_substring", SubstringFn);
+    RegisterFunction("stdout", StdoutFn);
+    RegisterFunction("sleep", SleepFn);
+
+    RegisterFunction("less_than_int", LessThanIntFn);
+    RegisterFunction("greater_than_int", GreaterThanIntFn);
+}
+
+
+// -----------------------------------------------------------------
+//   convenience methods for functions
+// -----------------------------------------------------------------
+
+// Evaluate the expressions in argv, giving 'count' char* (the ... is
+// zero or more char** to put them in).  If any expression evaluates
+// to NULL, free the rest and return -1.  Return 0 on success.
+int ReadArgs(State* state, Expr* argv[], int count, ...) {
+    char** args = reinterpret_cast<char**>(malloc(count * sizeof(char*)));
+    va_list v;
+    va_start(v, count);
+    int i;
+    for (i = 0; i < count; ++i) {
+        args[i] = Evaluate(state, argv[i]);
+        if (args[i] == NULL) {
+            va_end(v);
+            int j;
+            for (j = 0; j < i; ++j) {
+                free(args[j]);
+            }
+            free(args);
+            return -1;
+        }
+        *(va_arg(v, char**)) = args[i];
+    }
+    va_end(v);
+    free(args);
+    return 0;
+}
+
+// Evaluate the expressions in argv, giving 'count' Value* (the ... is
+// zero or more Value** to put them in).  If any expression evaluates
+// to NULL, free the rest and return -1.  Return 0 on success.
+int ReadValueArgs(State* state, Expr* argv[], int count, ...) {
+    Value** args = reinterpret_cast<Value**>(malloc(count * sizeof(Value*)));
+    va_list v;
+    va_start(v, count);
+    int i;
+    for (i = 0; i < count; ++i) {
+        args[i] = EvaluateValue(state, argv[i]);
+        if (args[i] == NULL) {
+            va_end(v);
+            int j;
+            for (j = 0; j < i; ++j) {
+                FreeValue(args[j]);
+            }
+            free(args);
+            return -1;
+        }
+        *(va_arg(v, Value**)) = args[i];
+    }
+    va_end(v);
+    free(args);
+    return 0;
+}
+
+// Evaluate the expressions in argv, returning an array of char*
+// results.  If any evaluate to NULL, free the rest and return NULL.
+// The caller is responsible for freeing the returned array and the
+// strings it contains.
+char** ReadVarArgs(State* state, int argc, Expr* argv[]) {
+    char** args = (char**)malloc(argc * sizeof(char*));
+    int i = 0;
+    for (i = 0; i < argc; ++i) {
+        args[i] = Evaluate(state, argv[i]);
+        if (args[i] == NULL) {
+            int j;
+            for (j = 0; j < i; ++j) {
+                free(args[j]);
+            }
+            free(args);
+            return NULL;
+        }
+    }
+    return args;
+}
+
+// Evaluate the expressions in argv, returning an array of Value*
+// results.  If any evaluate to NULL, free the rest and return NULL.
+// The caller is responsible for freeing the returned array and the
+// Values it contains.
+Value** ReadValueVarArgs(State* state, int argc, Expr* argv[]) {
+    Value** args = (Value**)malloc(argc * sizeof(Value*));
+    int i = 0;
+    for (i = 0; i < argc; ++i) {
+        args[i] = EvaluateValue(state, argv[i]);
+        if (args[i] == NULL) {
+            int j;
+            for (j = 0; j < i; ++j) {
+                FreeValue(args[j]);
+            }
+            free(args);
+            return NULL;
+        }
+    }
+    return args;
+}
+
+// Use printf-style arguments to compose an error message to put into
+// *state.  Returns NULL.
+Value* ErrorAbort(State* state, const char* format, ...) {
+    char* buffer = reinterpret_cast<char*>(malloc(4096));
+    va_list v;
+    va_start(v, format);
+    vsnprintf(buffer, 4096, format, v);
+    va_end(v);
+    free(state->errmsg);
+    state->errmsg = buffer;
+    return NULL;
+}