PS: add step3_env

6 files changed, 157 insertions, 13 deletions

diff --git a/docs/TODO b/docs/TODO
index f530ef0..3c3df97 100644
--- a/docs/TODO
+++ b/docs/TODO
@@ -49,7 +49,7 @@ Java:
 
 Postscript:
     - negative numbers
-    - step 3-A
+    - step 4-A
 
 Rust:
     - http://www.rustforrubyists.com/book/index.html
diff --git a/ps/step0_repl.ps b/ps/step0_repl.ps
index 325392f..1085525 100644
--- a/ps/step0_repl.ps
+++ b/ps/step0_repl.ps
@@ -24,9 +24,7 @@
 
 
 % repl
-/REP {
-    READ (stub env) EVAL PRINT
-} def
+/REP { READ (stub env) EVAL PRINT } def
 
 /stdin (%stdin) (r) file def 
 
diff --git a/ps/step1_read_print.ps b/ps/step1_read_print.ps
index 8c54012..d08579c 100644
--- a/ps/step1_read_print.ps
+++ b/ps/step1_read_print.ps
@@ -26,9 +26,7 @@
 
 
 % repl
-/REP {
-    READ (stub env) EVAL PRINT
-} def
+/REP { READ (stub env) EVAL PRINT } def
 
 /stdin (%stdin) (r) file def 
 
diff --git a/ps/step2_eval.ps b/ps/step2_eval.ps
index 60d1906..72a91fa 100644
--- a/ps/step2_eval.ps
+++ b/ps/step2_eval.ps
@@ -12,6 +12,7 @@
 /eval_ast { 2 dict begin
     /env exch def
     /ast exch def
+    %(eval_ast: ) print ast ==
     /nametype ast type eq { %if symbol
         env ast get
     }{ /arraytype ast type eq { %elseif list
@@ -25,15 +26,16 @@
     } ifelse } ifelse
 end } def
 
-/EVAL { 5 dict begin
+/EVAL { 3 dict begin
     /env exch def
     /ast exch def
+    %(EVAL: ) print ast ==
     /arraytype ast type ne { %if not a list
         ast env eval_ast
     }{ %else apply the list
         /el ast env eval_ast def
-        el 1 el length 1 sub getinterval % args array
-        el 0 get cvx % function
+        el _rest % args array
+        el _first % function
         %(vvv\n) print pstack (^^^\n) print
         exec % apply function to args
     } ifelse
@@ -56,9 +58,7 @@ end } def
     (/) { dup 0 get exch 1 get idiv }
 >> def
 
-/REP {
-    READ repl_env EVAL PRINT
-} def
+/REP { READ repl_env EVAL PRINT } def
 
 /stdin (%stdin) (r) file def 
 
diff --git a/ps/step3_env.ps b/ps/step3_env.ps
new file mode 100644
index 0000000..c2e65cb
--- /dev/null
+++ b/ps/step3_env.ps
@@ -0,0 +1,98 @@
+(types.ps) run
+(reader.ps) run
+
+% read
+/READ {
+    /str exch def
+    str read_str
+} def
+
+
+% eval
+/eval_ast { 2 dict begin
+    /env exch def
+    /ast exch def
+    %(eval_ast: ) print ast ==
+    /nametype ast type eq { %if symbol
+        env ast env_get
+    }{ /arraytype ast type eq { %elseif list
+        [
+            ast {
+                env EVAL
+            } forall
+        ]
+    }{ % else
+        ast
+    } ifelse } ifelse
+end } def
+
+/EVAL { 10 dict begin
+    /env exch def
+    /ast exch def
+    %(EVAL: ) print ast ==
+    /arraytype ast type ne { %if not a list
+        ast env eval_ast
+    }{ %else apply the list
+        /a0 ast 0 get def
+        /def! a0 eq { %if def!
+            /a1 ast 1 get def
+            /a2 ast 2 get def
+            env a1  a2 env EVAL  env_set
+        }{ /let* a0 eq { %if let*
+            /a1 ast 1 get def
+            /a2 ast 2 get def
+            /let_env env env_new def
+            0 2 a1 length 1 sub { %for each pair
+                /idx exch def
+                let_env
+                    a1 idx get
+                    a1 idx 1 add get let_env EVAL
+                    env_set
+            } for
+            a2 let_env EVAL
+        }{
+            /el ast env eval_ast def
+            el _rest % args array
+            el _first cvx % function
+            %(vvv\n) print pstack (^^^\n) print
+            exec % apply function to args
+        } ifelse } ifelse
+    } ifelse
+end } def
+
+
+% print
+/PRINT {
+    /exp exch def
+    %(printing: ) print exp ==
+    exp pr_str
+} def
+
+
+% repl
+/repl_env null env_new def
+
+/REP { READ repl_env EVAL PRINT } def
+/_ref { repl_env 3 1 roll env_set pop } def
+
+(+) { dup 0 get exch 1 get add } _ref
+(-) { dup 0 get exch 1 get sub } _ref
+(*) { dup 0 get exch 1 get mul } _ref
+(/) { dup 0 get exch 1 get idiv } _ref
+
+/stdin (%stdin) (r) file def 
+
+{ % loop
+    (user> ) print flush
+
+    %(%lineedit) (r) file 99 string readline
+    stdin 99 string readline
+
+    not { exit } if  % exit if EOF
+
+    %(\ngot line: ) print dup print (\n) print flush
+    REP print (\n) print
+} bind loop
+
+(\n) print  % final newline before exit for cleanliness
+quit
diff --git a/ps/types.ps b/ps/types.ps
index 2201cd4..5028c58 100644
--- a/ps/types.ps
+++ b/ps/types.ps
@@ -67,3 +67,53 @@
     %pstack
     %(pr_str2 stack ^^^\n) print
 } def
+
+
+% list operations
+/_first { 0 get } def
+/_rest { dup length 1 sub 1 exch getinterval } def
+/_nth { get } def
+
+
+%
+% Env implementation
+%
+/env_new { 1 dict begin
+    /outer exch def
+    << 
+        /__outer__ outer
+    >>
+end } def
+
+/env_find { 2 dict begin
+    /key exch def
+    /env exch def
+    env key known { %if key in env
+        env
+    }{ env /__outer__ get null ne { %elseif __outer__ not null
+        env /__outer__ get   key env_find
+    }{ %else
+        null
+    } ifelse } ifelse
+end } def
+
+/env_set { 3 dict begin
+    /func dup xcheck def
+    /val exch cvlit def
+    /key exch def
+    /env exch def
+    env key val func { cvx } if put
+    val func { cvx } if
+end } def
+
+/env_get { 2 dict begin
+    /key exch def
+    /env exch def
+    env key env_find
+    dup null eq {
+        (Error: ') print key 99 string cvs print (' not found\n) print
+        error
+    }{
+        key get
+    } ifelse
+end } def