evaluator | 易学教程

Mutually recursive evaluator in Haskell

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问题 Update: I've added an answer that describes my final solution (hint: the single Expr data type wasn't sufficient). I'm writing an evaluator for a little expression language, but I'm stuck on the LetRec construct. This is the language: type Var = String type Binds = [(Var, Expr)] data Expr = Var Var | Lam Var Expr | App Expr Expr | Con Int | Sub Expr Expr | If Expr Expr Expr | Let Var Expr Expr | LetRec Binds Expr deriving (Show, Eq) And this this the evaluator so far: data Value = ValInt Int

Java String and Mathematical Expression Evaluators

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问题 We use the Jeks parser at present to evaluate expressions. I cannot see a way to evaluate string expressions with it - for example: IF( "Test 1" = "Test 2") Is there anything out there that can evaluate string and mathematical expressions in Java? Preferably free or open source. Thanks for any help, Andez 回答1: There are a lot of tools out there to evaluate expressions; the correct answer will depend on your exact goals. Two things that I'd look at: Commons EL, which evaluates JSP 2.0

Prolog evaluator that uses previously solved information as input

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问题 I have written a program that takes a parse tree as input and evaluates it. It works when the identifiers in the tree do not reoccur. I want the evaluator to take in multiple statements, and use the values assigned to identfiers when I solve later statements. Here is my program. add_op --> ['+']. assign_op --> ['=']. ident(ident(Ident)) --> [Ident], {atom(Ident)}. /* True if an identifier */ int(int(Int)) --> [Int], {integer(Int)}. /* True if an integer */ semicolon --> [';']. evaluator

Java String and Mathematical Expression Evaluators

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We use the Jeks parser at present to evaluate expressions. I cannot see a way to evaluate string expressions with it - for example: IF( "Test 1" = "Test 2") Is there anything out there that can evaluate string and mathematical expressions in Java? Preferably free or open source. Thanks for any help, Andez There are a lot of tools out there to evaluate expressions; the correct answer will depend on your exact goals. Two things that I'd look at: Commons EL , which evaluates JSP 2.0 expression language . Rhino , which evaluates JavaScript (I think this is part of JDK 1.6, but haven't used it as

glEvalCoord when used with glFeedback is not giving output as expected

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I am trying to read the value from glEvalCoord, but not getting the exact values which I should get. My code is GLfloat ctrlpoints[4][3] = { { -4.0, -4.0, 0.0}, { -2.0, 4.0, 0.0}, { 2.0, -4.0, 0.0}, { 4.0, 4.0, 0.0}}; void display() { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); glEnable(GL_LIGHTING); glMap1f(GL_MAP1_VERTEX_3, 0.0, 1.0, 3, 4, &ctrlpoints[0][0]); glEnable(GL_MAP1_VERTEX_3); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); GLint size; GLfloat feedBuffer[1024]; glFeedbackBuffer (1024, GL_3D, feedBuffer); glRenderMode (GL_FEEDBACK); glBegin (GL_POINTS); for (int i=0; i<=30; +

glEvalCoord when used with glFeedback is not giving output as expected

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问题 I am trying to read the value from glEvalCoord, but not getting the exact values which I should get. My code is GLfloat ctrlpoints[4][3] = { { -4.0, -4.0, 0.0}, { -2.0, 4.0, 0.0}, { 2.0, -4.0, 0.0}, { 4.0, 4.0, 0.0}}; void display() { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); glEnable(GL_LIGHTING); glMap1f(GL_MAP1_VERTEX_3, 0.0, 1.0, 3, 4, &ctrlpoints[0][0]); glEnable(GL_MAP1_VERTEX_3); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); GLint size; GLfloat feedBuffer[1024];