PS: step2_eval

4 files changed, 90 insertions, 4 deletions

diff --git a/docs/TODO b/docs/TODO
index 32036fd..f530ef0 100644
--- a/docs/TODO
+++ b/docs/TODO
@@ -48,7 +48,8 @@ Java:
     - step9_interop
 
 Postscript:
-    - step 1-A
+    - negative numbers
+    - step 3-A
 
 Rust:
     - http://www.rustforrubyists.com/book/index.html
diff --git a/ps/reader.ps b/ps/reader.ps
index 4be0c0f..0fa4c02 100644
--- a/ps/reader.ps
+++ b/ps/reader.ps
@@ -86,7 +86,8 @@
         exit % EOF
     }{
         /ch str idx get def  % current character
-        ch 48 ge ch 57 le and 45 ch eq or { %if number
+        %ch 48 ge ch 57 le and 45 ch eq or { %if number
+        ch 48 ge ch 57 le and { %if number
             str idx read_number
         }{ ch 34 eq { %elseif double-quote
             str idx read_string
diff --git a/ps/step2_eval.ps b/ps/step2_eval.ps
new file mode 100644
index 0000000..60d1906
--- /dev/null
+++ b/ps/step2_eval.ps
@@ -0,0 +1,78 @@
+(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
+    /nametype ast type eq { %if symbol
+        env ast get
+    }{ /arraytype ast type eq { %elseif list
+        [
+            ast {
+                env EVAL
+            } forall
+        ]
+    }{ % else
+        ast
+    } ifelse } ifelse
+end } def
+
+/EVAL { 5 dict begin
+    /env exch def
+    /ast exch def
+    /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
+        %(vvv\n) print pstack (^^^\n) print
+        exec % apply function to args
+    } ifelse
+end } def
+
+
+% print
+/PRINT {
+    /exp exch def
+    %(printing: ) print exp ==
+    exp pr_str
+} def
+
+
+% repl
+/repl_env <<
+    (+) { dup 0 get exch 1 get add }
+    (-) { dup 0 get exch 1 get sub }
+    (*) { dup 0 get exch 1 get mul }
+    (/) { dup 0 get exch 1 get idiv }
+>> def
+
+/REP {
+    READ repl_env EVAL PRINT
+} def
+
+/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 a9d5023..2201cd4 100644
--- a/ps/types.ps
+++ b/ps/types.ps
@@ -1,7 +1,5 @@
 (in types.ps\n) print
 
-/MAX_SYM_SIZE 256
-
 % concatenate: concatenate two strings or two arrays
 % From Thinking in PostScript 1990 Reid
 % (string1) (string2) concatenate string3
@@ -24,6 +22,14 @@
     % stack: new
 } bind def
 
+% reverse: array1 -> reverse -> array2
+/reverse {
+    [ exch
+    aload % push array onto stack
+    length -1 0 { 1 roll } for % reverse
+    ]
+} def
+
 /pr_str {
     %(in pr_str\n) print
     /obj exch def